J2gpp

- [Feature] Filter to throw J2GPP warning or error from template, with Jinja2 fork only
- [Doc] Document the warning and error filters, also in the scripting section
- [Fix] Wildcard with --filter or --test won't catch directories causing errors
- [Fix] No exception error if alignment block doesn't contain any marker
- [Fix] Write and append filter are render_time_only as well
- [Fix] Include statement paths are relative to template

- [Doc] Add table of content to Readme

- [Doc] Document usage of J2GPP for scripting

The jump to version 2 is marked by the intention of enabling more scripting within J2GPP templates.

- [Feature] Can skip generating rendered source file when using the `write`or `append` filters

- [Fix] Correctly left-justify with ljust filter

- [Feature] Extra tests from Python default functions
- [Fix] Lines without any § do not affect column width for other lines