SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

- Enabled MAP_JIT on x86_64 after confirming that pthread_jit* calls are only
required for MAP_JIT pages on Apple Silicon

In MacOS 11.2 mprotect can no longer change the access protection settings of
pages that were previously marked as executable to anything but PROT_NONE. This
commit works around this new restriction by bypassing the mprotect based write
protection and instead relying on the write protection provided by MAP_JIT.

- Added MacOS version checking around MAP_JIT to prepare code for x86 MAP_JIT

Analytics:
- Incorporated fix to allow the full set of analytics that was recommended by
  spotlightishere

BuildMacOSUniversalBinary:
- The x86_64 slice for a universal binary is now built for 10.12
- The universal binary build script now can be configured though command line
  options instead of modifying the script itself.
- os.system calls were replaced with equivalent subprocess calls
- Formatting was reworked to be more PEP 8 compliant
- The script was refactored to make it more modular
- The com.apple.security.cs.disable-library-validation entitlement was removed

Memory Management:
- Changed the JITPageWrite*Execute*() functions to incorporate support for
  nesting

Other:
- Fixed several small lint errors
- Fixed doc and formatting mistakes
- Several small refactors to make things clearer