Add abi offset

[ShawnYun]

close #207

1. Modify the optimizer to record the method entry offset when optimizing code.
2. Offset of method entry is added when generating abi file.
3. Remove the auto-insert main method when generating abi file.

@lightszero @shargon @Tommo-L Could you help review the code?

[lightszero]

this codes make people confused,
we could do better.

we could let optimizer ouput a label addrConvTable.do not let optimizer to parse module direct.

[lightszero]

@ShawnYun I just clear optimizer, check it please and continue.
I think we need a unittest for it too.

[lightszero]

sorry addrconvtable has bug,only convert labels,I will fix it.

[ShawnYun]

@lightszero Thanks, It's better now.

[ShawnYun]

Now we can use _engine.ExecuteTestCaseStandard("method_name", arg1, arg2, arg3) to invoke contract method.

[Tommo-L]

It's ready for review, @lightszero @shargon could help review it.

[lightszero]

looks good for me,

but conflict by #253

please fix it

[ShawnYun]

@lightszero Thanks, Have fixed it.

[shargon]

Why these tests was removed?

[shargon]

https://github.com/neo-project/neo-devpack-dotnet/pull/252/files#r415749579

This should not have been merged if it didn't work with the unit test, the solution is not to comment the code that doesn't work.

[ShawnYun]

@shargon Sorry, I will restore them after I fix the Parser_DeleteDeadCode.