new convenient interface for creating addresses

To create an address from a public key or script, you used to have to do the
hashing yourself, and find the version yourself. For example:

var hash = bitcore.util.sha256ripe160(pubkey);
var version = bitcore.networks['livenet'].addressVersion;
var addr = new Address(version, hash);

But with this interface, things are much simpler:

var addr = Address.fromPubKey(pubkey);

The new convenience methods are:

Address.fromPubKey (for regular pubkeyhash addresses)
Address.fromPubKeys (for p2sh multisig addresses)
Address.fromScript (for any p2sh address)
update fromPubKeys to use fromScript

This means fewer code-duplication. Also added another test for fromScript to
make sure it is thoroughly tested. Also pass through opts to createMultisig so
that you can choose to lot let it be sorted if you want.
Merge pull request #237 from ryanxcharles/feature/address-interface

new convenient interface for creating addresses