Option to allow hash character ('#') to appear in user part of SIP URL

[bennylp]

By default, hash character will be escaped as per RFC 3261 rule. Unfortunately some endpoints want this character in the user part of a request.

This ticket adds a run-time option to allow hash character to appear in user part of SIP URL of outgoing requests. Sample code:

pjsip_cfg()->endpt.allow_tx_hash_in_uri = 1;