Added the Time base library

[LiuShao.chain]

Should we add a time base?

Implement similar to JavaScript getFullYear()、getMonth()、getDate()

In some scenarios involving real world time, but also need to be used in smart contracts, we often need it.

We have an on-chain timestamp to get the on-chain time, and we lack an entry point to get a day directly.

[marco.chain]

I would like to get more opinions on that, especially from Sophia devs (cc @radrow.chain, @ghallakaeternity.chain, @hanssv.chain).

in the sophia examples repo there is an old example for a DateTime lib, see:

• aepp-sophia-examples/contracts/Libraries/lib/DateTime.aes at master · aeternity/aepp-sophia-examples · GitHub

tests are here:

• aepp-sophia-examples/test/libraryUsage.js at master · aeternity/aepp-sophia-examples · GitHub

[hanssv.chain]

Sorry, forgot to write here - discussed it with @radrow.chain directly.

This sounds like a good library to have in the compiler if you ask me.