added get method to transport to allow send via flow feature

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
moved sequential search logic from transaction layer to sip.create.

This way next hop calculation is gathered in one place (previously
next hop calculation for client transactions was in
transaction.createClientTransaction and for transactionless 'ACK'
in sip.create)

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
Added Path header parser and stringifier

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
Implemented support for flow selection via Route header

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
Added extension parameter sip.makeResponse

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
proxy.js: fixed CANCEL request route handling

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
changed parser to parse AOR uris in 'Route', 'Record-Route' and 'Path' headers

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
Return right reason (430) in case of failed flow

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>
Added simple example of websocket enabled proxy (examples/websocket-proxy.js)

Signed-off-by: Kirill Mikhailov <kirill.mikhailov@gmail.com>