Upgrade gem dependencies
Remove comments not adding any value
There's no upper limit for integer settings
s/MiniTest/Minitest/
Normalizing code style
Reduce linecache dependency
Clean up command output a bit
Remove unused method
callstyles should be strings, not symbols
Complete review of the test suite

* Use standard minitest instead of minitest/spec. I find it more
concise, extendable and readable.
* Various simplifications, fixes and rewordings here and there.
Move a couple of utility methods to a better place
Whitespace fix
Remove annoying warning

An empty backtrace may actually make sense for threads in the "aborting"
state
Skip threading tests until I can have a look
Fix some test names
Fixes #71

Just needed to check for nil method_id values to prevent the segfault