By default, those expression use the application's locale. The addition of an optional
language parameter allows handling of dates that wouldn't match that default
locale (say for e.g. an English system running QGIS trying to transform a
French-formatted string into a date object).
A new script then parses these json help files into the html help
contents, in a standardised manner. Previously, the function help
was a bunch of different formats and structures.
Now, a custom stylesheet can be applied (and later tweaked!) to
format these help. Eg, this commit colors variables and function
names in the syntax section for greater readability.
