Add method and add classmethod tag

[PeterlitsZo]

Set get_part as a classmethod, and add method get_parts

For: #36, #45

[coveralls]

Coverage remained the same at 100.0% when pulling a5e9f91 on PeterlitsZo:patch-1 into 7d146bd on stefankoegl:master.

[PeterlitsZo]

Well, I will fix it.

[PeterlitsZo]

How can I deal with coverage? I think I need some help~

[PeterlitsZo]

Do I need to update tests.py?

[PeterlitsZo]

Looks great! but method get_part's usage changed. If you want to pull this, I think it is better to change version.

[stefankoegl]

Thanks for the contribution!

but method get_part's usage changed.

Do you see any case that was valid before but is failing now? It should still be ok to call the classmethod from an instance, right?

[PeterlitsZo]

OMG, you are so smart. Right at total!

[stefankoegl]

Thanks for your contribution :)