New stun_servers and turn_servers parameters
Add 'Content-Length' header to every SIP response

..,whether or not it carries a body

- For interaction with implementations that require responses to have this header.
Merge remote-tracking branch 'upstream/master'
This is no longer version "0.2.1" but "devel".
Add URI and NameAddrHeader classes
Add JsSIP.URI and JsSIP.NameAddrHeader classes
Fix typo
Add 'stun_servers' and 'turn_servers' configuration parameters

Which allow setting multiple stun and turn servers
Cosmetic change.

- Uppercase 'C' (constants), 'Utils', and 'Exceptions' module names.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/MediaSession.js
	src/UA.js