Scenario documenting multiple exclude

This adds a scenario that explicitly shows how excluding examples with
multiple tags should behave. I.e `-t ~skip -t ~speed:slow`
Merge pull request #775 from sorentwo/document-multi-exclude

Scenario documenting multiple exclude
Fix Example#instance_eval to properly forward args.

It's not used very often, but it was blowing up from the pretty print library:
Small typo on README for described_class()

Should be described_class() instead of described()
Merge pull request #780 from elgalu/patch-1

Small typo on README for described_class()
README uses expect() syntax
Merge pull request #782 from banyan/readme-uses-expect-syntax

README uses expect() syntax
Preserve the original state of ARGV by duplicating the array. Closes #787
Merge pull request #788 from csmuc/dup_command_line_args

Preserve the original state of ARGV by duplicating the array. Closes #787
Regenerate html fixtures for ruby 2.0.
Use new Codeclimate badge, made by @olivierlacan
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Merge pull request #791 from pjambet/use_new_codeclimate_shield

Use new Codeclimate badge, made by @olivierlacan
Ruby 2.0 is green.
fix typos and improve wording
Merge pull request #797 from glyn/master

Editorial changes to the main readme
Update changelog for release
2.13.0 release
Use hook classes as proxies rather than extending hook blocks.

* Fixes #799.
Changelog for #799 [ci skip]
Improve on 0c56b9b3e5dc1b5457814db1de31032ca012f839.

- The options state really belongs with the hook when the instance is created.
  Better to pass it in the initializer than to have a separate `with` method
  for setting it.
- No need to wrap/unwrap the block with a proc an extra time; we can just
  pass the proc directly into the initializer.