Fix `.byebugrc` priority

Settings in project's `.byebugrc` should override those in global (home
folder) `.byebugrc` file.
Use previously defined variables
Remove non-standard message
More extensive next/step tests
Always mantain real stack size in the C extension
Rename rake task and require it in Rakefile
Enforce code style in the C extension
Cleanup travis config

Compilation is included in the default task so that line is not
necessary.
Some love to the CHANGELOG
Add CCop to the build
Move test to more standard location
Finish up fix for #93

Use the actual number of items in the backtraces as the backtrace size
instead of the (less reliable) calculated value.
Add small comment
Fix backtraces crashing in c-frames

I don't get why this was previously working... :S
Remove unnecessary variable
Whitespace