added Measurement#localize method which converts a unit to the unit used in the current locale
local units are stored in a :unitwise element of the yaml locale file, using the atom property as the key eg

:uk
  :unitwise
    length : m

:us
  :unitwise
    length : ft

the localize method will search the Atom database for a unit with the same dimensions so it can work out the property to
use for a compound term

if no translation is available the original Measurement is returned

also added flow rate (liter/hour) to derived rate
Merge branch 'rails_integration' of https://github.com/steveg-h/Unitwise into rails_integration

Conflicts:
	lib/unitwise/measurement.rb