Listing all currencies

[augustusnaz]

Since the currencies entity object does not contain fully named currency values, can we have a list method?
Would simply return an array of all currencies in the same format as get .

[steffanhalvorsen]

I would accept a PR for this if you want to. It should not be hard to implement, but I got very limited time right now.

[chathurabuddi]

@steffanhalvorsen nice library, I'll work on this and submit a PR. Please assign ticket to me