FloatField is translated differently between supported implementations
Thanks.

Floats, by definition, should only take 4 bytes.

_Currently:_
- SQLite, real, 8 bytes
- MySQL, double precision, 8 bytes
- PostgreSQL, real, 4 bytes

_Proposal:_
- SQLite should continue using real (I believe there is no 4 bytes floating point datatype).
- MySQL should be using float, 4 bytes.
