Move configuration class from matchers to expectations.

- It's general config for rspec-expectations, not
  just for the matchers and fits better there.
- This allows us to cleanup some odd cross-requires
  where rspec/expectations files were requiring
  rspec/matchers files and vice-versa.
- The attribute for this remains on RSpec::Matchers
  because that's where rspec-core looks for it and
  that's been the public API.
Leverage the optimized require logic from rspec-support.

Closes #464
Add changelog entry.

[ci skip]
cleanup ws
[skip ci]
Merge pull request #488 from rspec/use-optimized-require

Use optimized require
Ensure `expect`, `should` and `should_not` are doc'd properly.

They should be doc'd as part of `RSpec::Matchers` and
`BasicObject`, not part of `RSpec::Expectations::Syntax`.
Fix comma splice
Merge pull request #492 from kchien/comma_splice

Fix comma splice
Updated travis build scripts (from rspec-dev)
Merge pull request #497 from rspec/update-travis-build-scripts-2014-03-14-for-master

Updates from rspec-dev (2014-03-14)