Correct outdated cop message (fixes #226)
Add new cop BlockNesting

It checks whether you've nested too many if/while/etc. blocks
which increase the cyclomatic complexity.
Replace `===` with `is_a?`
Merge pull request #228 from emou/nesting-levels-cop

Add new cop BlockNesting
Add --require option to inject external Ruby code into RuboCop
Add Offence#cop_name
Rework report classes into formatters
Add -f/--format option to specify formatter
Deprecate -e/--emacs option
Add -o/--out option to specify output file
Refactor and style
Enable multiple formatters
Enable use of custom formatter class
Always pass absolute file paths to formatters

Previously, paths of files searched by RuboCop were absolute,
but paths which are directly specified in command line args were not.
Add YARD documentation of public formatter APIs