Added option '--interface-strip'

This option can be used to strip custom prefixes from interface
names. Defaults to 'wl_'.
Add option '--interface-prefix'

A custom prefix can be specified with this option which will be
prepended to interface names after stripping to generate the final class
name.
Append _ to all argument names to avoid name clashes

This commit fixes wrapper generation for the wl_subcompositor interface.
The request get_subsurface takes two wl_surface arguments resulting in
ambiguous code when the wl_ prefix is stripped.

Now all arguments to requests and events include an extra _ to avoid
these kind of bugs in the future.