Add support for getblockchaininfo rpc cmd

-sync.supply setting now allows getting moneysupply from getblockchaininfo cmd
-README updated with info abour getblockchaininfo cmd

lib/nodeapi.js

@@ -43,6 +43,7 @@ module.exports = function() {
         case 'getrawtransaction':
         case 'getsupply':
         case 'getinfo':
+        case 'getblockchaininfo':
         case 'getpeerinfo':
         case 'gettxoutsetinfo':
         case 'getmaxmoney':
@@ -156,6 +157,7 @@ module.exports = function() {
         case 'getconnectioncount':
         case 'getblockcount':
         case 'getinfo':
+        case 'getblockchaininfo':
         case 'getpeerinfo':
         case 'gettxoutsetinfo':
         case 'getvotelist':