Fixes things like:
* exported type/method/function X should have comment or be unexported
* comment on exported type/method/function X should be of the form "X ..."
(with optional leading article)
Refs. #213.
neo-storm has developed more wrappers for syscall APIs, so they can and should
be used as a drop-in replacement for pkg/vm/api. Moving it out of vm, as it's
not exactly related to the VM itself.
* new mapping for interop api
* Fixed interop API mapping + added missing apis
* added engine apis
Imported from CityOfZion/neo-storm (ec5e6c8e2b587704a1e071e83b633d2d3a235300).
