Add support for passing local files to server as raw data

[huard]

Overview

This PR fixes #96

Changes:

• Added support for path to local files ('/...' and 'file:///')
• Added support for file-like object (BaseIO)
• Added support for Path instances
• If server is localhost and Path to file is local, send reference
• Updated documentation and notebook

Test suite requires bird-house/emu#74

[cehbrecht]

added comments to the code.

[huard]

Does OWSLib know when to tag content with CDATA ? As long as we're passing trivial text and base64, we're good, but if not, that could become a problem.

[cehbrecht]

owslib does not automatically use cdata encoding for complex inputs:
https://github.com/geopython/OWSLib/blob/dcbc8db9a8eafa715a0469317bf23ea07de17326/owslib/wps.py#L1619

We may prepare this in birdy. But probably we would like to move the encoding part to owslib (base64, raw, cdata, ...). The encoding is decided by the mime-type.

[cehbrecht]

Just to reference comments in pywps PR:
geopython/pywps#444

[cehbrecht]

... codacy complain belongs to this PR.

Unused urljoin imported from six.moves.urllib.parse

[cehbrecht]

@huard fixed urljoin import and run successfully manual tests. Shall I merge?