Added __getstate__ and __setstate__ to classes with __slots__ so they can be pickled.
Update common.py

Adjusted minimal order size for btc_eur and btc_rur
Merge pull request #29 from Jazzer9F/patch-1

Thanks!
Updated minimal order size for btc_eur and btc_rur.
Merge branch 'master' into py3
Ported last changes to Py3 with 2to3-3.2