Introduce force framework and convert VariableInspector into a force

The force framework allows cops to share common logic and reduce wasted
CPU power by module mixins. A force implements custom processing and
invokes some hooks in cops that belong to the force.
[#934] New cop UnderscorePrefixedVariableName
Fix an offense reported by UnderscorePrefixedVariableName
Merge pull request #979 from yujinakayama/underscore-prefixed-variable-name

New cop UnderscorePrefixedVariableName
failing test case for UnderscorePrefixedVariableName
Fix infinite correction in IndentationWidth

The solution is to not report indentation offenses in blocks where
the end/} does not start the line that it's on.

Closes #975.
update LineEndConcatenation description
Merge pull request #983 from jonas054/fix_infinite_correction

Fix infinite correction in IndentationWidth
Merge pull request #984 from mockdeep/concat_desc

update LineEndConcatenation description
Fix false positive with zsuper in UnderscorePrefixedVariableName

This fixes #982.
Merge pull request #985 from yujinakayama/fix-underscore-prefixed-variable-name-with-zsuper

Fix false positive with zero-arity super in UnderscorePrefixedVariableName
[Fix #490] Add EnforcedStyle config option to TrailingBlankLines
Remove FinalNewline cop

It is no longer needed. The same check is done by TrailingBlankLines.
Remove special logic for avoiding TrailingWhitespace clobbering

This is done on a higher level now, so no need to do it in the cops.
Merge pull request #991 from jonas054/configurable_trailing_blank_lines

Configurable trailing blank lines
Add missing full stop
Add auto_correct task to Rake integration
Merge pull request #989 from irrationalfab/feature-rake-auto-correct

Add auto_correct task to Rake integration
[Fix #992] Correct a typo
Improve Debugger's message