Add haml-spec to tests after other tests

See #656.

If `haml-spec/ruby_haml_test.rb` is the first test file to be loaded by
Rake, Haml is loaded without Rails already being loaded. This means
`haml/railtie` isn't loaded which causes some test failures that expect
it to have been.

Explicitly add `haml-spec/ruby_haml_test.rb` after the "normal" test
files so this doesn't happen.

Conflicts:
	Rakefile
Don't test Ruby 1.8.7 with Rails 4+
Remove unused @params in docs

`tabs` and `options` parameters to `fix_textareas!` have been removed,
see 71bda112041c52b89dce3f626bf38636bb6e2181 and
2efd12f27e3d5e60bcbe1b34a9507518262747e4.
Update links to options in REFERENCE.md

Update links that haven't been updated after change in options handling.
Update :ruby filter docs in REFERENCE.md

Ruby filter no longer writes stdout to the document. Update REFERENCE.md
to reflect this.
Minor formatting / whitespace
Go back to allowing failures on Rubinius
optimize capture_haml line to create fewer objects
Updated changelog