Add basic support for custom tags

[mauricioabreu]

Main parser function now receives a function that can be
used to parse the line content and save it into the data store object.

[coveralls]

Coverage decreased (-0.8%) to 96.353% when pulling 5f40195 on mauricioabreu:parse-custom-tags into 6cbe1e5 on globocom:master.

[mauricioabreu]

I have another idea here: we can add the "ignored" tags in a new data structure, containing the line, lineno and any other useful information that can be directly used by m3u8 users after they parse the content.

...
        elif line.startswith('#'):
            data['ignored_lines'] = {'line': line, 'lineno': lineno}
...

# Usage
m3u8_obj = m3u8.loads('#EXTM3U8 ... etc ... ')
data = post_process_data(m3u8_obj.data)

[leandromoreira]

LGTM and solves #123 and #124 does all the tests pass locally @mauricioabreu ? I tried to restart the build manually but the same error happened

 Plugin 'pytest_cov' could not be loaded:

[leandromoreira]

fix build

[mauricioabreu]

@leandromoreira I was reading about this error and it seems to be incompatibility of python version vs pytest_cov plugin. One way to solve this issue is using tox: https://tox.readthedocs.io/en/latest/

[mauricioabreu]

Python 3.5 and Python 2.6 passed the test suite: https://travis-ci.org/globocom/m3u8/builds/485545837?utm_source=github_status&utm_medium=notification

[leandromoreira]

so I'll merge it and then I'll try to use this tox thing.

[mauricioabreu]

@leandromoreira we don't pin versions of any dependence. Recently pytest_cov deprecated some python versions as we can see here: https://github.com/pytest-dev/pytest-cov/blob/master/setup.py#L127

python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*'

Maybe tox can help us to define different dependency versions for different python versions.

[leandromoreira]

We should do this.

[leandromoreira]

good catch