* Add otpion to skip building and testing Android libraries
Add `skip.android=true` to the local.properties files at the project's root to skip Android builds.
* Each native library is in its own jar. Got rid of cross compilation. The project is `secp256k1` and not `secp256k1-kmp`.
* Updated CI to use all 3 OS VMs
Co-authored-by: Salomon BRYS <salomon@kodein.net>