A warning is enough, don't crash

Calculated vs real backtraces are still inconsistent in some edge
cases. In those cases, we are already showing a warning from the ruby
library so I'm just removing this raise from the C extension cause it's
not expected when it happens.
Space between argument and default value
Set default argument instead of explicit nil
Add parenthesis in some method calls for clarity
Small refactor of "errmsg" method
Fix style & some rubocop offenses
Extract breakpoint stuff to its own class
Small refactor in condition command
Refactor get_int helper method
Remove some unnecessary stuff
Move assignment until actually used
Whitespace
Those are actually errors
Refactor
More refactoring
Extract some behaviour to a new method
Keep fixing rubocop stuff
Output is line-oriented, so use puts
Remove unnecessary throw/catch
Remove FIXME that won't get fixed