Indentation support

[hnisula]

Automatic indentation seems to require some code style implementation to be supported.

[hnisula]

Implementing, and registering, a FormattingModelBuilder along with ASTBlock/Block enables both reformatting of the file but also auto-indent on enter. After some experimentation it could perhaps be possible to do most formatting through simple code just looping AST elements and then handle the special cases for indentation and perhaps more.

Plan B could be to do specific handling of each element in some elements (where loops are not specific enough).

[hnisula]

The PyBlock is probably a good sample to follow. It diverges from the tutorial (which says basically nothing and does not seem to work as expected) so it should work and having been used in real life.