Metadata-parser

this bump introduces 2 new arguments and some changed behavior:

- `search_head_only=None`. previously the meta/og/etc data was only searched in the document head (where expected as per HTML specs).
after indexing millions of pages, many appeared to implement this incorrectly of have html that is so off specification that
parsing libraries can't correctly read it (for example, Twitter.com).
This is currently implemented to default from None to True, but future versions will default to `False`.
This is marked for a future default of `search_head_only=False`

- `raise_on_invalid`. default False. If True, this will raise a new exception: InvalidDocument if the response
does not look like a proper html document

- more aggressive attempts to get the peername.

- this will now try to cache the `peername` of the request (ie, the remote server) onto the peername attribute

- applying a `strip()` to the "title". bad authors/cms often have whitespace.

- added kwargs to docstrings
- `get_metadata_link` behavior has been changed as follows:
* if an encoded uri is present (starts with `data:image/`)
** this will return None by default
** if a kwarg of `allow_encoded_uri=True` is submitted, will return the encoded url (without a url prefix)

- merged https://github.com/jvanasco/metadata_parser/pull/9 from xethorn
- nested all commands to `log` under `__debug__` to avoid calls on production when PYTHONOPTIMIZE is set