New xgettext method for i18n module

This method call xgettext to extract translatable
string from source files into a .pot translation template.

It differs from a plain CustomTarget in three ways:
- It accepts build targets as sources, and automatically resolves source
  files from those build targets;
- It detects command lines that are too long, and writes, at config
  time, the list of source files into a text file to be consumed by the
  xgettext command;
- It detects dependencies between pot extraction targets, based on the
  dependencies between source targets.

1 files changed, 12 insertions, 0 deletions

diff --git a/docs/markdown/snippets/i18n_xgettext.md b/docs/markdown/snippets/i18n_xgettext.md
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+## i18n module xgettext
+
+There is a new `xgettext` function in `i18n` module that acts as a
+wrapper around `xgettext`. It allows to extract strings to translate from
+source files.
+
+This function is convenient, because:
+- It can find the sources files from a build target;
+- It will use an intermediate file when the number of source files is too
+  big to be handled directly from the command line;
+- It is able to get strings to translate from the dependencies of the given
+  targets.