JSON-RPC

Changes made in this pull-request:

- jsonrpc api with all methods available from javascript-api
- added cors headers to jsonrpc
- separated libethrpc
- Javascript jsonrpc client, with the same interface as Javascript bindings in EthereumBrowser, so there is now possibility to run/debug code using eth object in Chrome/Firefox and other browsers
- here is a playground - https://github.com/debris/eth-client-example
- added async setters/getters for javascript properties
- tests for most of jsonrpc methods

* api is not yet unified with Go client api
from javascript api you can now call 
```javascript
eth.coinbase = 'xxxx';
```
or async
```javascript
eth.setCoinbase('xxxx', _fn)
```
and both of these methods uses this "private" method to actually set the coinbase;
and since, there is also javascript jsonrpc client, with the same API, i do not want people to use methods, which are not available in one of these APIs.