Simplified some bracket scope functions

sublime.Regions are not immediately needed while tuples are more
convenient, so region constructors now return simple tuples.

Filtering also is unnecessary, we need to just label scopes with
respect to priorities, not simply split them up into classes.
Added sketch bracket coloring

The code is obviously rough at the moment, but the algorithm choice
and implementation are pretty much completed.

There are several things that I want to improve before merging this
into master:

  - make proper configuration interface

  - add missing docstrings, comments

  - code style cleanup in general

  - term cleanup in general (e.g., extents? maybe they are 'spans')

  - implement merging of the consecutive lines

After this, I believe, I will leave the actual coloring as a stub
and move on to configuration jobs: reading, parsing, processing,
generating color scopes, etc.
Moved the configuration into a separate module

Not expressively happy with it, still could be improved, but for now
this should be somewhat okay.
Code style fixes

- exposed `outer/inner_index` from bracket_scopes
- exposed `extent` from bracket_coloring
- fixed function names and some usage
- added more docstrings
Implemented merging of the consecutive current lines
Added test visual demonstation of the coloring
Merged branch 'coloring-scopes'

Now the coloring algorithms are also in their place. Time to tackle
Sublime scope generation, settings/configuration management, etc.

Also I would like to use proper Python types (instead of easy-to-use
but hard to read ad-hoc tuples) for all those 'regions', 'scopes'
and so on. Currently looking into how it can be done with maximum
readability and minimum class-defining and __meta__ boilerplate.