Refactor ABI lib

[trinhdn2]

Resolve issue #387
Require PR #385 to be merged first

This PR fixes a few issues:

• If there is no return in a call function, unpack should return nil error
• For some functions which have struct array as parameter, it will also be detected and generate the struct definition
• For the event, if it has a non-indexed parameter, the parameter name will also be assigned if empty. Also the internal struct will be detected and generate struct definition if not exist.
• Fix annotation generation in the event function

Besides, this PR uses internalType information to generate struct binding. The internalType is introduced in solidity v0.5.11 which represents the raw name of struct.