Allow loader to accept non-strings

[clbarnes]

etree is old and so doesn't accept py3.4's pathlib.Path.
parsexml_ now calls str() on non-strings to work around this and other
similar os.PathLikes.

[clbarnes]

The 3.5 failure should be fixed by #81.

The 2.6 failure is because 2.6 has been EOL since I was in undergrad. See #79.

[clbarnes]

This has been rebased on #81 to fix the 3.5 failure.

[clbarnes]

Hmm. Is this PR even mergeable, as nml.py is generated code? The changes will just break next time it's generated; so it's really a problem with generateDS.py.

[pgleeson]

Thanks for these changes @clbarnes, i'll look at them over the next few days.

An update to the version of generateDS might solve some of the problems.. Alternatively a small script for a standard search/replace to post process the nml.py should suffice, with instructions added here: https://github.com/NeuralEnsemble/libNeuroML/blob/development/neuroml/nml/README.md.

[clbarnes]

Thanks, I'll look into that. I think my commits are all in the wrong order now I've realised editing nml.py is the wrong way to go, so I'll close these PRs and cherry-pick the other changes.

[clbarnes]

Just FYI I have raised a PR on generateds which should allow this the next time the code is regenerated.

https://bitbucket.org/dkuhlman/generateds/pull-requests/45/make-parsexml_-compatible-with-ospathlike/diff

[clbarnes]

The generateds PR has been merged https://bitbucket.org/dkuhlman/generateds/commits/8ee5214bd106 , don't know when it'll make it into a release though.

[pgleeson]

Thanks @clbarnes. Have tested the latest generateDS locally with libNeuroML and it looks like it works fine. Will check through your other changes as soon as I get a chance.

[clbarnes]

Worth noting that the changes to generateDS will only allow it to work with Paths in python 3.6 up. It will still work with strings in anything lower than that.