Make PowerAssert::Context private
Trivial changes
Add missing test
Support ruby-level operator method calls
Extend PowerAssert.start to take a block for getting ref values
Duplicate methods to prevent side effects
Reduce costs for searching method_ids
Disable optimization

TracePoint doesn't fire return/c_return event on specialized instructions
Cosmetic changes
Support :command_call
Support string, regexp interpolation
Add test-unit to development dependency
Link to test-unit-power_assert
Add .travis.yml so travis-ci.org could build it