Changing current AoS representation of datatypes to SoA

[vidsinghal]

Currently spending time refactoring the type signature of LocVar.
goal 1: get the AoS representation working with the new LocVar type.
goal 2: modify inferLocations to factor out new locations for fields.
...

[ulysses4ever]

A big chunk of the patch so far is replacing string literals like "loc1" with ("loc1", []). This could be done automagically if the following 3 conditions hold:

1. LocVar was made into a proper datatype. (It should be anyway)
2. LocVar was made an instance of the IsString class.
3. The OverloadedStrings GHC extension was activated (maybe it already is? I haven't checked).

For the common case where you want to turn a non-literal String into LocaVar, there should be a "smart constructor", i.e. a function that turns a string into LocVar:

single :: String -> LocaVar
single s = (s, [])

and you should use it throughout.