Allow passing snowflake proxyURL as a SOCKS arg
This will make it easier for calling applications to pass outbound proxy information to the Snowflake library. Non-tor applications and applications such as Orbot that run PTs in a separate process can now configure outbound proxies without setting tor-specific environment variables.
This is a followup to !63 (merged), and necessary for github.com/tladesignz/IPtProxy/pull/61