2.1.0

Enforce varname formatting for CODEMIRROR_FIELD_INIT_JS setting so it
should always be a valid Javascript variable name.

Concretely varname is slugified and dashes are replaced by underscores so
a given varname like foo codemérror-0 is turned to foo_codemerror_0.

This should be a safe change and resolve issues with usages inside a formset.
Thanks to @abumalick for report.

Also added support with Django 2.2 and removed notices about major changes
from 2.0.0 version.

2.0.0

Add support for Django 1.11, 2.0, 2.1 and CodeMirror 5.40.2

• Rewrite package to use setup.cfg;
• Add support for Django 1.11, Django 2.0 and Django 2.1, close #22;
• Drop support for Django 1.8 and 1.9;
• Django 1.11 support is the last one for Python2;
• Change old demo project to more cleaner sandbox;
• Change widget to use new Django widget API;
• Upgraded included copy of CodeMirror to 5.40.2;