Issue 193: Reference Update

A number of the IETF drafts referenced now have updated versions, so that the reference section should be updated with a pointer to the latest versions and dates.

In addition, new terminology relating to transport modes has been introduced in the AVTEXT WG Grouping Taxonomy document, and probably should be referenced informatively.

Proposed changes:

In Section 1.1, change:

"The term SST-SS refers to an SVC implementation that transmits all layers within a single RTP session, using a single SSRC. The term SST-MS refers to an SVC implementation that transmits all layers within a single RTP session, using a distinct SSRC for each layer."

To:

"The term SRST, defined in [GROUPING] Section 3.7, refers to an SVC implementation that transmits all layers within a single RTP session, using a single SSRC. The term MRST, defined in [GROUPING] Section 3.7, refers to an SVC implementation that transmits all layers within a single RTP session, using a distinct SSRC for each layer."

Add the following informative reference:

[GROUPING]
J. Lennox; K. Gross; S. Nandakumar; G. Salgueiro; B. Burman. RTP Grouping Taxonomy. 05 March 2015. Internet Draft (work in progress). URL: https://tools.ietf.org/html/draft-ietf-avtext-rtp-grouping-taxonomy