[Fix #1441] Compare AST for whole buffer in AutocorrectUnlessChangingAST

We were already re-parsing the whole buffer to check for syntax
errors. If we check for AST equality instead, we don't need to
check the syntax.
Merge pull request #1443 from jonas054/1441_blocks

[Fix #1441] Compare AST for whole buffer in AutocorrectUnlessChangingAST
Mention RuboCop for RubyMine
Include HTML Formatter report example
Merge pull request #1446 from joventuraz/master

Update README adding HTML formatter
[Fix #1181] Don't report strings in interpolations in StringLiterals

Second fix for 1181. Strings inside interpolations are
handled by StringLiteralsInInterpolation, to StringLiterals should
stay away from them.
Merge pull request #1447 from jonas054/1181_string_lit

[Fix #1181] Don't report strings in interpolations in StringLiterals
[Fix #1427] Exclude top level directories early

Take the excluded top level directories out of the equation
altogether so that they are not searched for files. This
is an optimization to speed up the target file search phase
when there is, for example, a vendor directory with a lot
of files in it (a top level vendor directory is excluded
by default).
Merge pull request #1448 from jonas054/1427_target_finder_perf

[Fix #1427] Exclude top level directories early
New cop Style/ElseNil

Checks for explicit `nil` in otherwise empty else-clauses. This is redundant, as
`nil` is returned by default if no other clause matches.
Rename ElseNil -> EmptyElse
Make empty else-clauses count as offences

Also, make use of `OnNormalIfUnless`.

Also, register the offence on the `else` keyword.