Rename checkBalance and listMarketPandL Functions

[phillc73]

The functions checkBalance and listMarketPandL should be renamed to match the naming convention used in the Betfair API calls, for consistency with the rest of the library.

Specifically that is:

• checkBalance to getAccountFunds
• listMarketPandL to listMarketProfitAndLoss

Old function names should re-direct to new function names for backwards compatibility.

[Soccerama]

Completely agree with this proposed change and had thought the same thing myself. My only reservation was the backwards issue but a simple redirect should manage that.

[phillc73]

Completed with commit 19f6688