Split VariableInspector inner classes into multiple files

Also rename VariableEntry to Variable.
Track usage of each assignment in UnusedLocalVariable

The cop now tracks usage of each assignment
rather than usage in entire variable lifetime.

This closes #458.
Fix crashes at class definition subclassing class stored in a lvar
Reorganize UnusedLocalVariable and UselessAssignment

* Extracted useless setter call tracking part of UselessAssignment to
  UselessSetterCall.
* Renamed UnusedLocalVariable to UselessAssignment.
Merge pull request #469 from yujinakayama/reassigned-but-unused-variable

Track usage of every assignment in UnusedLocalVariable
Improve highlight range of UselessAssignment
Suggest using _ as a variable name for useless multiple assignment
Suggest using normal operator for op-assignment at the end of scope
Add AlignHash.
Make RuboCop code pass AlignHash inspection.
Merge pull request #470 from yujinakayama/improve-useless-assignment

Improve offence report of UselessAssignment
Merge pull request #471 from jonas054/fix_auto_corr_param_indent

Add AlignHash cop.
[Fix #466] Make AvoidGlobalVars configurable
The cop now has a config option called `AllowedVariables`.
It also accepts by default built-in JRuby global variables.
[Fix #463] Allow arg destructuring in ReduceArguments cop
Fix a typo
Fix bug concerning table alignment of colon separated hash entries.

Table alignment required the colon to be detached from the key, which
is a syntax error.

Also, colon and hash rocket are not mixed in the specs anymore. We don't
have full support for that kind of mix, so let's not make readers believe
that we do.

I have some changes lined up to take care of concerns raised in #471,
but first I want to add this bugfix.
Merge pull request #476 from jonas054/fix_align_hash

Fix bug concerning table alignment of colon separated hash entries.
Remove special AlignHash setting in lib/rubocop/formatter.

Use the default setting "key" instead of "separator".
Support separate configuration in AlignHash for => and : style.
Extend README a bit