Validate ABI function name and signatures

[BellringerQuinn]

so that we throw an argument exception and make it easier to diagnose a common issue where users were providing an ABI in the wrong format

[pkieltyka]

nice work.. I think even better.. just port the code https://github.com/0xsequence/ethkit/blob/master/ethcoder/events_parser.go#L38

to C# .. as you will see, its just string manipulation.

I propose name the function, ParseABISelector instead of ParseEventDef.. I think that "selector" is a better name for this, as its for functions and events.

then, you can handle any input and it will just work, it wont error for users :)

its 350 LOC