gettext*: update to 0.21.

Version 0.21 - July 2020

* Programming languages support:
  - Shell:
    o xgettext now recognizes and ignores 'env' invocations and environment
      variable assignments in front of commands.
  - Java:
    o xgettext now recognizes format strings in the Formatter syntax.  They
      are marked as 'java-printf-format' in POT and PO files.
    o xgettext now recognizes text blocks as string literals.
  - JavaScript:
    xgettext parses JSX expressions more reliably.
  - Ruby:
    o xgettext now supports Ruby.
    o 'msgfmt -c' now verifies the syntax of translations of Ruby format
      strings.

* Runtime behaviour:
  - On native Windows platforms, the directory that contains the message
    catalogs may now contain arbitrary Unicode characters. To make use of
    this feature, use the new function 'wbindtextdomain' instead of
    'bindtextdomain'. It allows to pass a directory name in wchar_t[] encoding.
    Note: 'wbindtextdomain' exists only on native Windows platforms.

* Improvements for translators:
  - When msgfmt writes a MO file, it now does so in such a way that processes
    that are currently using an older copy of the MO file will not crash.

* Libtextstyle:
  - Added support for emitting hyperlinks.
  - New API for doing formatted output.
  - The example programs support the NO_COLOR environment variable.


(wiz)