Adding functionality for Full Currency Name look up

[con-dev123]

What is the purpose of your pull request?

As per Issue: https://github.com/Alir3z4/python-currencies/issues/12

To add functionality to the main class whereby you can get the full currency name.

Important

• Added JSON file to 'currencies' folder called "currency_name.json"
• This JSON file is a basic key/value setup
• Most of these full name values should be the official/correct ones
• Source is mainly Google preview after search, as well as https://www.worlddata.info/currencies

Useage

from currencies import Currency

currency = Currency('USD')

currency.getname()

>>> 'United States Dollar'

Other Info

Resolves https://github.com/Alir3z4/python-currencies/issues/12 which can be closed now

[con-dev123]

Oh additionally, this is my first time contributing to a project so I'm not 100% sure I've done the fork/merge etc etc right

Please excuse anything I've missed :)