Licensing.parse: Raise ExpressionParseError instead of ParseError

[carmenbianca]

Fixes #35.

I also removed the except TypeError statement inside of the method. It didn't appear to do much that I could see. It didn't light up any tests when I removed it, either.

ExpressionParseError is a subclass of both ParseError and
ExpressionError. This allows the user to do `except ParseError`
as they had done before, and nothing will break. If the user does
`except ExpressionError`, the ParseErrors will now also be caught.

The advantage of doing this is that `except ExpressionError` now
catches all exceptions coming out of this method.

This is therefore a breaking change.

Signed-off-by: Carmen Bianca Bakker <carmen@carmenbianca.eu>

[carmenbianca]

This Python 3.6 test is broken: https://travis-ci.org/nexB/license-expression/jobs/535835832

Not sure why, but pyenv install -s 3.6.1 fails.

The Python 2 tests are also broken because I use raise ... from. That should be an easy fix if you want to keep Python 2 compatibility, but Python 2 is almost EOL.

[pombredanne]

@carmenbianca Thank you ++
We definitely want to keep this compatible with Python2 for now, if anything at least until ScanCode is ported to Python 3 (which is something that will happen soon, starting next week as a GSoC-sponsored project).

As for the Pyenv issue, sounds like the pyenv version on macOS is old... and your forced usage of Python 3 idioms brought that issue to light!

The solution would be to update pyenv to the latest version as part of CI run.

[carmenbianca]

I have changed the code to be compatible with Python 2.7

I unfortunately do not know how to solve the pyenv issue.

[pombredanne]

Sounds like we are affected by travis-ci/travis-ci#9929

[pombredanne]

@carmenbianca while @Abhishek-Dev09 is working out a way yo get Azure pipelines for proper testing on Scancode (that we can then reuse here too), I am merging this anyway as this should not be held by these issues.

[pombredanne]

Thank you ++