[opus] SPEEX and OPUS questions and minor issues

[dos386]

Thanks ...

> Those links seem to work here.

2 links "http://rarewares.hydrogenaudio.org" redirect
to "https://hydrogenaud.io" ... no "rarewares" subdomain

"http://git.xiph.org/speex.git" maybe better
"http://git.xiph.org/?p=speex.git;a=summary"

"http://git.xiph.org/speexdsp.git" maybe better
"http://git.xiph.org/?p=speexdsp.git;a=summary"

"http://speex.org/roadmap" maybe just delete it?

> splitting the resampler into its own lib, however it's not clear
> if it would really be worth it.

well ... so split off SpeexDSP docs at least

>an easy-ish task for a newcomer to tackle

Let me know what obvious needs to be written or proof-read.