Code cleanup

[noryb009]

There are a few changes I want to make to clean up the code:

• [ ] Switch to 2 spaces for indents.
• [x] Don't use relative paths in includes (and rename utils.*).
• [x] Rename C++ files to use a more common extension (either cpp or cc).
• [ ] Use a better plugin style (ideally just dropping in a cpp file would be enough to add it). This makes it really easy to add extensions, it's not a game of trying to figure out what lines need to be added where.
• [ ] Use bools instead of ints.
• [ ] Where we can't use ints, standardize what ints mean (eg. sometimes 0 is an error, sometimes -1 is an error).