
This method updates the account of an authority for an exisiting account.

Warning: You can create impossible authorities using this method. The
method will fail if you create an impossible owner authority, but will
allow impossible active and posting authorities.

Parameters:
    account_name: The name of the account whose authority you wish to
	update (type: const string &)
    type: The authority type. e.g. owner, active, or posting (type:
	authority_type)
    auth_account: The account to add the the authority (type: const string
	&)
    weight: The weight the account should have in the authority. A weight
	of 0 indicates the removal of the account. (type: weight_type)
    broadcast: true if you wish to broadcast the transaction. (type: bool)
