Document that extra ether is abandoned

Abandoning extra ether is fine for simplicity: this policy should be documented though.

Examples:
SingularDTVFund.sol has no fallback function on purpose
And of course this can't be prevented https://github.com/ConsenSys/smart-contract-best-practices#remember-that-ether-can-be-forcibly-sent-to-an-account
Related to #64

Review SingularDTVFund.sol and the linked smart-contract best-practices guidance first. Document that extra ether is intentionally abandoned, including that the contract has no fallback function and that ether can still be forcibly sent; done means the policy is recorded in the project's appropriate documentation.

Written by the indexing model from the issue text.