Exception Classes Roundup

[rbeyer]

Description

• Created a new exceptions.py module and grouped all pvl Exceptions there.
• Altered the message that LexerError emits to provide context around the character that caused the error.
• Added bump2version configuration file.

Motivation and Context

Would close #58

How Has This Been Tested?

• make lint
• make docs
• make test-all

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Licensing:

This project is released under the LICENSE.

• I claim copyrights on my contributions in this pull request, and I provide those contributions via this pull request under the same license terms that the pvl project uses.

[michaelaye]

just to let you know, if you want to fight config file proliferation, that bump2version can be configured via a section in setup.cfg.

[rbeyer]

@michaelaye yeah, I don't have a strong feeling about it right now, so I just added it as a separate file.