Implement ignore and UTF-8

docs/LOCALE.md

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+Locale Considerations
+=====================
+
+The editline library has basic support for locales via the use of the standard
+POSIX functions `mbrtowc` and `wcwidth`.  As a result, the on-screen width of
+characters in printed text should be calculated correctly, the so-called 
+[East Asian ambiguous][] characters being a notable exception.
+
+  [East Asian ambiguous]: http://www.unicode.org/reports/tr11/tr11-38.html
+
+The input handling is not yet multibyte-aware. Specifically, the presence of
+non-self-synchonizing encodings requires always segmenting the whole string
+using `mbrlen` when deleting.
+
+Programs wishing to use the feature need to link to a build of `editline`
+configured with `--enable-locale`.  In addition, the program should call
+`setlocale(LC_CTYPE, "")` to use the locale settings of the environment.