Add Web API resources

[matthieu]

1. Create a category under Code for "Web APIs" and under that category, include the following text and associated links:
   WebHooks and WebSockets - http://dev.blockcypher.com/#websocket_webhook
   Creating Transactions - http://dev.blockcypher.com/#creating_transactions
2. Add the following free resources under the category API docs: full-node bitcoin cloud implementation - http://dev.blockcypher.com/
3. Add the following free resources under the category Code:
   Core - bitcoin: modularized with separated components (BlockCypher) - http://dev.blockcypher.com/
   Tools - block chain event notifications (BlockCypher) - http://dev.blockcypher.com/#events
   Clients - golang: bitcoin client rebuilt in Go (BlockCypher) - http://dev.blockcypher.com/
   Block Exploration - raw data for bitcoin and litecoin blockchains (BlockCypher) - http://dev.blockcypher.com/#blockchain-api

[JeremyRubin]

Agreed. Web API resources are important.

Also suggest adding Chain.com's API: https://chain.com/

[matthieu]

How about now? Want a pull request? The chain API doesn't exist anymore tho :)