Make a short coding style guide in the VTR developer guide

[vaughnbetz]

Initial ideas below. This shouldn't be too long, and should be reviewed by others to make sure we agree.

1. Write code that is easier for others to read.
2. Add big picture comments.

• New functions: Doxygen comment in .h file or on static declaration.
  Data structures / classes: comment overall use and every member.
  Files: comment overall purpose of file.

3. Meaningful variable names. Types usually start with a Capital (older code may not follow this).
4. Avoid long functions whenever possible (refactor into shorter routines).
   Details:
   Avoid overuse of auto (give rule)
   camel or snake case OK.

Proposed Behaviour

We have some basic coding guidelines written down.

Current Behaviour

We don't have a style guide. We also are gradually evolving some code style (e.g. types moving from t_ to start with a capital, and using references more and pointers less, using Doxygen comments).

Possible Solution

A short style guide under the VTR developer guide.