Update p12n extract and view (remove metro, OS portability)

p12n_extract:
* remove Metro control
* remove concatenations for paths, use os.path.join and os.sep
* fix coding style consistency (parenthesis, quotes, and instead of &)

Remove Metro from view
Merge pull request #266 from flodolo/metro_p12n

Update p12n extract and view: remove metro, improve OS portability