Build RAJA developers guide

[rhornung67]

Document our basic processes and coding guidelines. Helpful for on-boarding new team members, contributors, consistency, etc.

Specific things to add:
[ ] conventions for compile-time code selection macros (consistency)
[ ] conventions for C vs. C++ header file inclusion
[ ] convention for typedef vs. using foo = bar

[davidbeckingsale]

@rhornung67 did you want this to be part of the Sphinx docs, or a separate PDF?

[rhornung67]

It will be part of the sphinx docs. I need to do a bunch of cleanup first.

[davidbeckingsale]

Okay, sounds good.

[rhornung67]

Closing as out-of-date. Will resurrect with a new issue.