templater: add inheritance support to style maps
We can now specify a base map file:
__base__ = path/to/map/file
That map file will be read and used to populate unset elements of the
current map. Unlike using %include, elements in the inherited class
will be read relative to that path.
This makes it much easier to make custom local tweaks to a style.
#require docutils gettext
$ $TESTDIR/check-gendoc de
checking for parse errors
Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
warning: please have a space before :hg: