Decluttered repo root.

This will break the CMake config. Part of issue #6 work.
Moved user includes.
Updated CMake config.
API users no longer have to include all headers.

I thought it would involve a lot more changes, but this seems to work.
One issue is that C doesn't recognise the `class` keyword, but that
should be fine so long as CBash isn't used in a pure C program.
Updated manual build instructions.

To remind people to include the include headers in the new include
directory.
Merge pull request #9 from WrinklyNinja/reorganise-repo

Reorganise repo
A small readme is better than nothing.