Which greatly simplifies reuse of these packages (and they're expected to be
reused since real tokens implement standards and also add something of their
own) and allows to avoid effects like
doc_test.go:68:28: ambiguous selector neoContract.BalanceOf
when neo.Contract is used. Avoids duplication in NEP-11 implementation as
well.
Notice that int64 types are used for gas per block or registration price
because the price has to fit into the system fee limitation and gas per block
value can't be more than 10 GAS. We use int64 for votes as well in other types
since NEO is limited to 100M.
