Flatten the namespaces.

Remove:
* ftxui::screen
* ftxui::dom
* ftxui::component

Keep:
* ftxui

examples/component/input.cpp

@@ -7,8 +7,7 @@
 #include "ftxui/component/screen_interactive.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
-using namespace ftxui::dom;
+using namespace ftxui;
 
 class MyComponent : ComponentVertical {
  public:

examples/component/menu.cpp

@@ -6,8 +6,7 @@
 #include "ftxui/component/screen_interactive.hpp"
 
 int main(int argc, const char* argv[]) {
-  using namespace ftxui::component;
-  using namespace ftxui::screen;
+  using namespace ftxui;
   auto screen = ScreenInteractive::FixedSize(30, 3);
   Menu menu(screen.delegate());
   menu.entries = {L"entry 1", L"entry 2", L"entry 3"};

examples/component/menu2.cpp

@@ -8,8 +8,7 @@
 #include "ftxui/component/screen_interactive.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
-using namespace ftxui::dom;
+using namespace ftxui;
 
 class MyComponent : ComponentHorizontal {
   public:

examples/component/menu_style.cpp

@@ -6,8 +6,7 @@
 #include "ftxui/component/screen_interactive.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
-using namespace ftxui::dom;
+using namespace ftxui;
 
 class MyComponent : ComponentHorizontal {
   public:

examples/component/tab.cpp

@@ -7,8 +7,7 @@
 #include "ftxui/component/toggle.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
-using namespace ftxui::dom;
+using namespace ftxui;
 
 class MyComponent : ComponentVertical {
   public:

examples/component/toggle.cpp

@@ -8,8 +8,7 @@
 #include "ftxui/component/toggle.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
-using namespace ftxui::dom;
+using namespace ftxui;
 
 class MyComponent : ComponentVertical {
  public:

examples/dom/blink.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"This text is "),

examples/dom/bold.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"This text is "),

examples/dom/color.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       vbox(

examples/dom/dbox.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::dom;
-  using namespace ftxui::screen;
+  using namespace ftxui;
   auto document =
     dbox(
       frame(

examples/dom/dim.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"This text is "),

examples/dom/frame.cpp

@@ -7,8 +7,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::dom;
-  using namespace ftxui::screen;
+  using namespace ftxui;
   auto document =
     hbox(
       window(text(L" main frame ") | hcenter,

examples/dom/gauge.cpp

@@ -7,8 +7,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::dom;
-  using namespace ftxui::screen;
+  using namespace ftxui;
   using namespace std::chrono_literals;
 
   std::string reset_position;

examples/dom/inverted.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"This text is "),

examples/dom/package_manager.cpp

@@ -10,8 +10,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
 
   struct Task {
     std::wstring name;

examples/dom/separator.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::dom;
-  using namespace ftxui::screen;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"left-column"),

examples/dom/spinner.cpp

@@ -9,8 +9,6 @@
 int main(int argc, const char *argv[])
 {
   using namespace ftxui;
-  using namespace ftxui::dom;
-  using namespace ftxui::screen;
   using namespace std::chrono_literals;
 
   std::string reset_position;

examples/dom/style_gallery.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"normal")                           , text(L" ") ,

examples/dom/underlined.cpp

@@ -4,8 +4,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     hbox(
       text(L"This text is "),

examples/dom/vbox_hbox.cpp

@@ -5,8 +5,7 @@
 
 int main(int argc, const char *argv[])
 {
-  using namespace ftxui::screen;
-  using namespace ftxui::dom;
+  using namespace ftxui;
   auto document =
     vbox(
       hbox(

examples/print_key_press.cpp

@@ -6,15 +6,14 @@
 #include "ftxui/component/screen_interactive.hpp"
 #include "ftxui/util/string.hpp"
 
-using namespace ftxui::component;
+using namespace ftxui;
 
 class DrawKey : public Component {
  public:
-  DrawKey(Delegate* delegate)
+  DrawKey(Component::Delegate* delegate)
       : Component(delegate) {}
 
-  ftxui::dom::Element Render() override {
-    using namespace ftxui::dom;
+  Element Render() override {
     Children children;
     for (size_t i = std::max(0, (int)keys.size() - 10); i < keys.size(); ++i) {
       std::string code = "";