Clean up and refactor some things

Commit summary
=============
* Wrap MiniTest::Expectations instance methods
* Use expectations instance method wrapper in ForArg
* Use instance method wrapper in ForBlock
* Change to Minitest constant
* Change location of NO_ARG
* add Gemfile
* Run `bundle exec rake` in travis
* Add rake as a development dependency
* Remove version file
* Rename stream delimiters
* Include 1.9.2 in travis.yml
* Reorganize ExpectSyntax
* Update Readme with tested versions and impls