Setup rubocop

This setup of rubocop is very lenient to begin with. Some leniencies are
established in .rubocop.yml and other times rules are disabled
inline in the files. Over time, more rules should be enabled.
Merge pull request #1685 from rspec/enable-rubocop-fixed-up

Setup rubocop
Remove unneeded require.
Modularize NullColorizer

Other colorizers s.t. ConsoleCodes are module with module_functions.
NullColorizer was a class and the class does not respond to `wrap()`.
This patch fixes the mismatch.
Fix hash notation for Ruby 1.8
Clarify changelog entry.

[ci skip]
Merge pull request #1689 from tomykaira/modularize_NullColorizer

Modularize NullColorizer
cleanup and changelog for 1689
Fix typo in ExampleGroup comment
Merge pull request #1690 from zhangsu/patch-1

Fix typo in ExampleGroup comment
Fix regression in rake task pattern option.

Fixes #1691.
Shellescape rake task patterns.
Handle `pattern = ./path/to/spec.rb` as well.

For #1691.
Merge pull request #1692 from rspec/fix-rake-task-pattern-regression

Fix rake task pattern regression
3.1.0 release.
Bump version to 3.2.0.pre.
Fix another regression in rake task pattern handling.

This was reported by @aprescott: https://github.com/rspec/rspec-core/pull/1671#issuecomment-54623310.

The regression was originally introduced in #1653.
See also #1691 and #1692.
3.1.1 has been released.
Single glob patterns that start with ./ don't match any files.
Tweak for consistent whitespace.