py: use pre-compiled regexps

[blueyed]

Before:

% time python py/vimlparser.py autoload/vimlparser.vim |md5sum                                                                                                          ⟳(c) ⟳(m) 🐍?
861997350d8e69dc32937d77afb5b931  -
python py/vimlparser.py autoload/vimlparser.vim  3.21s user 0.07s system 99% cpu 3.282 total
md5sum  0.00s user 0.00s system 0% cpu 3.282 total

After:

% time python py/vimlparser.py autoload/vimlparser.vim |md5sum                                                                                                         🐍?
861997350d8e69dc32937d77afb5b931  -
python py/vimlparser.py autoload/vimlparser.vim  2.94s user 0.04s system 99% cpu 2.979 total
md5sum  0.00s user 0.00s system 0% cpu 2.979 total

[tyru]

This seems to be on the right track for me (except failing tests).
@vim-jp/vim-vimlparser what do you think about this?

[tyru]

@blueyed Is this PR necessary even after #142 ?