Refine the document of predefined custom matchers
Add a document on to_throw
Support :Expect expr { ... }
Define to_throw
Split test files on matchers
Add tests for to_throw
Update tests for internal changes
Merge branch 'exception-matchers'

Close gh-28.
Add release notes on 1.2.0
Bump up version to 1.2.0
Merge branch 'prepare-for-1.2.0'