build: Check package version in find_package (#643)

Modify the `ftxui-config.cmake.in` file so that it includes
`ftxui-targets.cmake`. This causes cmake to check the version is
compatible with what the user requested.

This patch also includes additional minor changes.

Co-authored-by: ArthurSonzogni <sonzogniarthur@gmail.com>

CHANGELOG.md

@@ -12,6 +12,9 @@ current (development)
 - Feature: `input` is now supporting multiple lines.
 - Feature: `input` style is now customizeable.
 
+### Build
+- Check version compatibility when using cmake find_package()
+
 4.1.0
 -----