Ensure consistent output across solc versions

[iamdefinitelyahuman]

Overview

I should be able to call compile_sources or compile_files with:

• any number of sources
• any combination of expected outputs
• any active version of solc

and get a consistent output format.

I should be able to look this output format up in the documentation.

Specification

1. Create parametrized unit tests to verify that output is consistent across versions.
2. Where there are inconsistencies, solve using common sense.
3. Document everything

Dependencies

Step one requires #53 .
Step three requres #52 .

[iamdefinitelyahuman]

Since #96 reduces the possible kwargs for the main compiler functions, this is now largely irrelevent. The wrapper might produce different outputs for different solc versions, but I think this can be considered expected when accessing the wrapper directly.