Add support for aarch64/arm64 architecture

[hrabid]

In arm64/aarch64 CPU, app detects the architecture of CPU & exits. Adding support for aarch64 will be really helpful specially for Raspberry PI & mobile users (mobile users use termux as terminal & apt package manager).
There is a libapt-pkg front-end called nala. Consider adding this package manager too.

[hkdb]

I don't currently have a raspberry pi or other arm64 devices to test with but I have changed the install and update scripts in v0.25 to let OS's that get "aarch64" from uname -m to use the arm64 build.

nala is currently not on the roadmap for me but I am always open to pull requests if anyone wants to help. I may however add pkg support in the future since I do use termux on my phones and am generally happy with pkg.

[hrabid]

I use termux heavily. Adding pkg will help a lot