Add makeTokenMint(), docs and tests

[mikemaccana]

Currently to make a token mint (with metadata) it's really damn long. Add a little wrapper function to do it in one line.

[mikemaccana]

Thanks for reviewing @ZYJLiu ! I've fixed the missing function to make the attributes, am now checking the account to read the attributes back from the unit tests, allowed users to use either objects or kv pairs for attrobutes, and made it return the new mint address rather than the function signature.