Support funcs

[tersec]

Currently, it throws an error:

nim-beacon-chain/vendor/nim-chronos/chronos/asyncmacro2.nim(161, 12) Error: Cannot transform this node kind into an async proc. proc/method definition or lambda node expected.

[cheatfate]

@tersec func is procedures without side effects (this means that the proc/iterator only changes locations that are reachable from its parameters and the return value only depends on the arguments).

But every {.async.} transformed procedure adds callbacks to thread-global system queue, so it exactly perform side effect. So its impossible.