rake clean/clobber

[eval]

This enables a clean and clobber task to help cleaning up any file created using the ragel namespace.

❯ be rake -T
rake build              # Build a gem file
rake clean              # Remove any temporary products
rake clobber            # Remove any generated files
rake corpus:verify_all  # Provide a LOCATION=/some/dir to verify parsing in bulk, otherwise defaults
rake ragel:generate     # Generate Ruby parsers from Ragel definitions
rake spec               # Run RSpec code examples