Singlefield

have a (first) look if you want @codingjoe 

test pass, everything works for me
decided to keep the original
- makes the definition easier (no need to fix digits and length)
- python `float` is not like the C float, it's more like the C `double` (with 53 bits of precision). So it's quite big. (see https://docs.python.org/2/tutorial/floatingpoint.html)
- it's mapped to a postgres `double precision` too (https://github.com/django/django/blob/ed7821231b7dbf34a6c8ca65be3b9bcbda4a0703/django/db/backends/postgresql_psycopg2/creation.py#L21) 
- it would make a possible migration from old to new far easier.