Add code formatting command

[thomas-bc]

Originating Project/Creator
Affected Component	fprime-util format
Affected Architectures(s)
Related Issue(s)	nasa/fprime#817
Has Unit Tests (y/n)	N
Builds Without Errors (y/n)	Y
Unit Tests Pass (y/n)
Documentation Included (y/n)	Y

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Change Description

Adds a new command to fprime-util to make using clang-format with FPrime source code easier (fprime-util format).

Rationale

This is mostly needed because of the access specifier macros in FPrime (e.g. PRIVATE:), which clang-format can't catch on, which resolves in bad formatting.
This new utility wraps around clang-format, replacing the macros before/after processing, and adding some functionality to make it easier to use with FPrime.

Testing/Review Recommendations

Usability is described in help_text.py -- can be easily tested within the core F' repo or any deployment, after a pip install .
Let me know if you can think of any feature/options that could be useful and I can try to add them in.