Fix GetBalances

Signed-off-by: Stéphane Depierrepont <toorop@toorop.fr>
Merge branch 'master' of https://github.com/Toorop/go-bittrex

# By Phil Song (5) and Dick Davies (1)
# Via Stéphane Depierrepont (2) and Dick Davies (1)
* 'master' of https://github.com/Toorop/go-bittrex:
  add fields to MarketSummary data
  fix newcandles format
  fix url parameter bug
  support new candeles
  support  bittrex candles
  support  bittrex candles