Add TIAS bandwidth type

[spscream]

Add TIAS support for sdp parsing.

I have the following sdp, which parsing is failed with ex_sdp, since TIAS isn't accepted:

v=0
o=- 3917959131 3917959131 IN IP4 192.168.1.95
s=pjmedia
b=AS:352
t=0 0
a=X-nat:0
m=audio 4008 RTP/AVP 8 0 18 101
c=IN IP4 192.168.1.95
b=TIAS:64000
a=rtcp:4009 IN IP4 192.168.1.95
a=sendrecv
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=ssrc:2014082431 cname:04970815321b4d3f
m=video 4010 RTP/AVP 99
c=IN IP4 192.168.1.95
b=TIAS:256000
a=rtcp:4011 IN IP4 192.168.1.95
a=sendrecv
a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=42e01e; packetization-mode=1
a=ssrc:277103621 cname:04970815321b4d3f
a=rtcp-fb:* nack pli