Remove or simplify regex in list-widgets and make-widgets commands

[ClmntBcqt]

Try to get the widgets (macros) with jinja engine directly.
Regex are hard to debug and maintain.

[ClmntBcqt]

For list-widgets command :

• Use of jinja2 parser to find all macros in files, list all files and all macros inside.

• Add a warning for ambiguous macro name (same macro name and filename)

For make-widgets command :

• Replace the command by a method in Document class, to not create an import file with all macros but directly write the imports before the body content of pages and post. It allow to have macro with same name in different files, and call them with filename.macroname(...).

• Add doc and an example.

[ClmntBcqt]

Merged in #44