Implemeted detection of bracket scopes

This is implemented and documented in `bracket_scopes` module.
A simple plugin that uses it is also implemented. However, for some
weird reason it hangs up Sublime when (Sublime) scope detection is
enabled. Currently looking into it...
Fixed 'unexplainable' Sublime hangup

Turned out to be a stupid infinite loop. No magic, go along.
Removed redundancy in the bracket search loop

Distinct `offset` and `point` are no longer needed.
Distinct `bracket` is no longer needed.
Removed redundant check in scope constructing

This actually never happens due to the nature of indices. Each left
bracket with a given index is uniquely associated with its matching
right bracket with the same index: it would be the closest one. Also,
there can be no other bracket pairs with the same index between two
matching brackets. There is no way we can mistake one right bracket
for another and incidentally mess up pairs. Thus the check can be
omitted.
Merged branch 'computing-scopes'

The roadmap for future work is like this:

  * coloring (think of possible algorithms, implement them)

  * reading the settings from the file

  * configuring colors via settings

  * adaptive scan window