Update please examples on front page

[yuchdev]

Basic example you provided is misleading (and does not work with TypeError: unsupported operand type(s) for /: 'float' and 'str')

my_bittrex = Bittrex(None, None, api_version=API_V2_0)  # or defaulting to v1.1 as Bittrex(None, None)
my_bittrex.get_markets()

It looks like Bittrex.__init__ has 3 first params key, secret, and version. However, init has more params:
def __init__(self, api_key, api_secret, calls_per_second=1, dispatch=using_requests, api_version=API_V1_1):