implement venom blocks

[charles-cooper]

it works by parsing the venom IR s-expr to IR, creating a builtin with a special name whose only job is to spit out that IR, and then creating a function call of that builtin to insert into the vyper ast

example usage:

(defn absoluteValue [] :external
   (venom "(seq (mstore (add 32 31) 5945936342127) (mstore 0 20) (return 0 0))")
)

[charles-cooper]

oh haha, just noticed there is an outstanding issue for this, fixes #1

[z80dev]

badass, thank you for your contribution