Requirement for high level API for SDP Attributes

Ref to RFC4566 section 6.  SDP Attributes.
We need high level parse for these following attributes which is common use in products.

```
a=rtpmap:<payload type> <encoding name>/<clock rate> [/<encoding
         parameters>]
```
```
a=fmtp:<format> <format specific parameters>
```
```
a=range:npt=<startTime>-<endTime>
```
also other range type