Add Out of Gas Vuln

[Evan Sultanik]

here is a real example: https://www.reddit.com/r/ethereum/comments/4ghzhv/governmentals_1100_eth_jackpot_payout_is_stuck/

[Evan Sultanik]

This looks like it's a similar attack; if not, add it as a separate example: https://github.com/ConsenSys/smart-contract-best-practices#dos-with-block-gas-limit

[Ben Perez]

Handled in #21