Reorganize data api endpoints

[martinkersner]

Datamaxi+ endpoints for candle and funding rate data have been updated. This PR reflects its changes and introduces a new API structure.

Candle

from datamaxi import Datamaxi

api_key = "YOUR API KEY"
maxi = Datamaxi(api_key=api_key)

# get supported exchanges for candle data (does not require API key)
maxi.funding_rate.exchanges()

# get supported symbols for binance spot market (does not require API key)
maxi.funding_rate.symbols("binance", market="spot")

# get supported intervals for binance spot market (does not require API key)
maxi.candle.intervals("binance", market="spot")

# get candle data for BTC-USDT futures market from binance in 1 day intervals
maxi.candle.get("binance", "BTC-USDT", "1d", "futures")

Funding Rate

from datamaxi import Datamaxi

api_key = "YOUR API KEY"
maxi = Datamaxi(api_key=api_key)

# get supported exchanges for funding rate data
maxi.funding_rate.exchanges()

# get supported symbols for binance exchange
maxi.funding_rate.symbols("binance")

# get funding rate data for BTC-USDT from binance
maxi.funding_rate.get("binance", "BTC-USDT")