Idea: #define usage for functions

Currently `#define` annotations are quite limited, being only applicable at the contract level.
It would be nice to be able to use a `#define`, rather than supplying a function, simply replacing the code inside other annotations.

Example:
```c++
#define voterId uint256 = voterList[_wallet]; // _wallet is a function parameter
#define voter Voter = listOfVoters[voterId];

#if_succeeds "registered the update"
voter.isActive == _isActive;
```

Would be translated into
```c++
#if_succeeds "registered the update"
listOfVoters[voterList[_wallet]].isActive == _isActive;
```

This would give `#define` a second purpose for functions and help clean up annotations.