Support for empty lines

[CarlosBorroto]

Hi, thanks for putting together this great library. It seems like currently it is not supporting empty lines which the spec allows:

Empty lines or lines that consist entirely of commas and/or whitespace characters are valid, but ignored.

Traceback (most recent call last):
  File "/snap/pycharm-community/62/helpers/pydev/pydevd.py", line 1664, in <module>
    main()
  File "/snap/pycharm-community/62/helpers/pydev/pydevd.py", line 1658, in main
    globals = debugger.run(setup['file'], None, None, is_module)
  File "/snap/pycharm-community/62/helpers/pydev/pydevd.py", line 1068, in run
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "/snap/pycharm-community/62/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/home/cborroto/projects/samplesheet/scripts/wdlhelper.py", line 210, in <module>
    main()
  File "/home/cborroto/projects/samplesheet/scripts/wdlhelper.py", line 205, in main
    'summary': summary,
  File "/home/cborroto/.pyenv/versions/miniconda3-4.3.30/envs/samplesheet/lib/python3.6/site-packages/fire/core.py", line 127, in Fire
    component_trace = _Fire(component, args, context, name)
  File "/home/cborroto/.pyenv/versions/miniconda3-4.3.30/envs/samplesheet/lib/python3.6/site-packages/fire/core.py", line 366, in _Fire
    component, remaining_args)
  File "/home/cborroto/.pyenv/versions/miniconda3-4.3.30/envs/samplesheet/lib/python3.6/site-packages/fire/core.py", line 542, in _CallCallable
    result = fn(*varargs, **kwargs)
  File "/home/cborroto/projects/samplesheet/scripts/wdlhelper.py", line 39, in launch
    sample_sheet = SampleSheet(sample_sheet)
  File "/home/cborroto/.pyenv/versions/miniconda3-4.3.30/envs/samplesheet/lib/python3.6/site-packages/sample_sheet/_sample_sheet.py", line 376, in __init__
    self._parse(str(self.path))
  File "/home/cborroto/.pyenv/versions/miniconda3-4.3.30/envs/samplesheet/lib/python3.6/site-packages/sample_sheet/_sample_sheet.py", line 468, in _parse
    header_match = self._section_header_re.match(line[0])
IndexError: list index out of range

[CarlosBorroto]

I just realized this is a duplicate and already fixed. Nevermind. Thanks.
#46

[clintval]

This was fixed with the feature request in #46 and the PR #47.

Right now the change is on master as I have not made a v0.7.0 release. I can try to get one in this week!

[clintval]

Ha, thanks for the reply! I'll get on the release this week.

[clintval]

Just made the release FYI.

pip install sample_sheet==0.7.0

[CarlosBorroto]

Thanks!