Transform

Creates a new Macro that allows you to define transformations from one thrift struct to another, where by default fields with the same name are copied from the source struct to the dst struct. It also allows for specifying functions to calculate the value for the specified dst field based on the src.

Example:
```
Macros.mkTransform[Types, SubTwo](
   ('intField,  (x: Types) => x.intField + 1),
    ('longField, (x: Types) => x.longField - 1)
)
```

I also did some tidy up to reduce the number of imports required in by maestro users.

Also deleted anything related to the Split macro since it isn't in use and has been superceded by the transform macro.
@quintona The problem are these 2 lines. You need to get the field name out of the AST into the macro code itself. So you can't depend on runtime values but only what is actually in the code itself. Happy to try and explain it better tomorrow.