An Ethereum coin flip contract
###About
This contract is intended to be used by other contracts and not necesariliy by end users. Using WeiFlip is made up of 2 contract calls made in sequence.
The coin flip is perfomed by providing the contract with a random_value and a blockNumber which must be at least n (default: 7) blocks in the future.
If sending value with your coin flip you must also pass in a heads_address and a tails_address to which all value will be sent depending on the outcome of the flip.
After n blocks anyone can call the reveal method with flipId (returned from previous call and stored in the contract) to have the relevant value sent to the appropriate address.