Allow specifying the Binance API URLs in env

[subos2008]

To allow for testing and development against mock / caching endpoints.

[coveralls]

Coverage increased (+0.1%) to 41.368% when pulling 55616df on subos2008:master into 852b256 on sammchardy:master.

[coveralls]

Coverage increased (+0.1%) to 41.368% when pulling 55616df on subos2008:master into 852b256 on sammchardy:master.

[coveralls]

Coverage increased (+0.1%) to 41.368% when pulling 55616df on subos2008:master into 852b256 on sammchardy:master.

[coveralls]

Coverage increased (+0.1%) to 41.368% when pulling 55616df on subos2008:master into 852b256 on sammchardy:master.

[sammchardy]

Hi @subos2008 if you check how I test, I use the requests_mock library to do this.

See examples here https://github.com/sammchardy/python-binance/blob/master/tests/test_api_request.py

[subos2008]

@sammchardy thanks for taking the time to look at this.

It's not testing I want to use this for.

To reduce the number of requests for historical klines data against the Binance API I have produced a transparent cache that replicates the Binance API. I want to be able to point your library at this caching endpoint rather than the exchange.

Hope that makes sense.