Map out include hierarchy

[camden-smallwood]

Noting that a header file is of extension .h/.hpp/.inc/.inl/etc, and a source file is of extension .c/.cpp/.cc/etc:

1. Currently all header files are lacking #include statements.
2. Source files also have a flattened list of #include statements, which is unnecessary.

It might be useful to store a mapping of each type's index to its declaring header file. This would allow for a list of all required #include statements to be generated for each header file. Once header files have their generated list of #include statements, then the flattened list of #include statements in each source file can be truncated (potentially) to only the required #include statements, allowing for carry-over #include statements from header files.