CMake Support, Clean-Up, Simplify Build Process

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This PR cleans the source code up a little and implements the following things:

• [x] Greatly simplified build process
• [x] Replace Makefiles with CMake
  • [x] Clean up build process
  • [x] Improves readability of build process
  • [x] Allows third-party projects to easily use AltServer as a library
• [x] Update Readme
  • [x] Build Instructions
  • [x] Minor Reformat

This PR also updates the patches to be compatible with latest upstream develop at time of writing (2ef20b3)

I've also adjusted the common.h, old-linux-polyfill.c and rewrite_altserver.py to fix some compilation errors I had.

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This build currently doesn't 100% work, I'll investigate the issue asap