Add a python generic function for handling Link header parsing

[karlcow]

We probably need to parse links in a few use cases for rewriting and/or sanitizing them. We have already two places we are doing that. Time for a refactoring.

See

webcompat.com/webcompat/helpers.py

Line 164 in 5ec17d8

def sanitize_link(link_header):

and

webcompat.com/webcompat/helpers.py

Line 142 in 5ec17d8

def rewrite_links(link_header):

[karlcow]

Some more complex libraries and more generic than ours.

• https://pypi.python.org/pypi/LinkHeader/
• https://gist.github.com/mnot/210535

But I think I will stick to something custom made. Experimenting and addting tests.

[karlcow]

Probably should use a map(our_func, iterable_links_list)