temporarily don't require rbx toolset & compiler gems

travis ci build fails as long as it doesn't have any rbx 2.0.0 binaries
available. once this is the case, we can uncomment this again
Merge pull request #75 from dirk/master

Bytecode implementation of Array#[]
Move bytecode implementations into lib/asm (follow-up to #75)
Add Module#overwrite_method:with_dynamic: to preserve docstrings
Add bytecode implementation of Integer#times:
Documentation and tests for Module#overwrite_method:with_dynamic:
Improve constant performance; add constant tests