add arm64 arch to support Apple M1

[kevintom]

• fix issue Support for ARM/M1 #87
• add arch definition
• update rake task to build binary
• update to a universal binary
• since M1 support only works on macOS 11+ versions I used lipo to create a universal binary as opposed to passing multiple arch argument flags to the compiler
• this way we can keep the x86_64 version working on earlier versions of macOS.
• I didn't recompile the x86 version, I simply used the exist version and merged it with the arm64 version.

first I renamed the x86_64 version

then I built an arm64 version using the current macOS Big Sur SDK

Next I renamed the arm64 version and I used lipo to produce a universal binary composed of the x86 version (compiled against the older SDK) and the arm64 (compiled against the current version of the SDK).

[kevintom]

i forgot to mention, that you could use lipo to in theory add more supported architectures to the universal binary.

if you compiled the older PPC or i386 versions (at their respectively supported SDK versions) you could lipo them together to this binary to make a 'really' universal binary such that the released gem binary would work on all the architectures.

that is probably the biggest difference in approach between this PR and #89

[PabloC]

+1 for this!

[PabloC]

This branch works great, please merge! :)

[ecnelises]

Needs adding the owner to reviewer?

[thibaudgg]

Hi @ecnelises, I plan to handle this over the weekend.
I don't have an M1 mac yet to test it myself so I will most likely just trust this PR, thanks all for your support. 👍🏻

[thibaudgg]

@kevintom version 0.11.0 has been released, thanks a lot for your work!