
Set the governance voting proxy for an account.

If a user does not wish to take an active part in governance voting, they
can choose to allow another account to vote their stake.

Setting a vote proxy does not remove your previous votes from the
blockchain, they remain there but are ignored. If you later null out your
vote proxy, your previous votes will take effect again (ABW: definitely not
true with regard to witness votes).

This setting can be changed at any time.

Parameters:
    account_to_modify: the name or id of the account to update (type: const
	string &)
    proxy: the name of account that should proxy to, or empty string to
	have no proxy (type: const string &)
    broadcast: true if you wish to broadcast the transaction (type: bool)
