Added basic parenting (lifetime management only, no transform hierarchy), using in perf_vis.
Starting to document, added Doxyfile.

- Added doxygen generation post build step.
Commenting.

- Doxygen gives an invalid warning if the enum macro in vertex.h is invoked using more than one.
    Could not reproduce in simple case.
Commenting components.
Commenting perf_vis.
Changed use of label to name for consistency (in profiling related classes). Commenting perf_vis.
Documenting and cleaning up perf_vis.
More commenting and minor changes to perf_vis.
Minor changes forgot to commit last commit.
Minor changes.

- Added features for perf_vis demo (bullet spam, reset).
- Working on adding control display for demo binaries.
Added quick hack so SDL_ttf will handle newlines in rendered text strings.
Added control display.