simplify regexp for macros
don't check input file suffix

It's not useful at all.
add another keyword
finish putting braces around macros (ignore macros with arg)

- remove re_keywords completely - not used
- parse `rpm --showrc' output to identify macros with argument
  (macro functions)
- parse processed spec file to identify macro functions, this is done within
  RpmSpecCleaner class so it can be called for multiple files