Draft: Updating Stream out documentation

Hello mentors :)

This MR is to update about the stream out, std, and transcoding documentation. I am creating the MR in my fork for getting the feedback and incorporating it, after which I will create the MR in the main repository. The new files created (and a few which are under progress) are listed below:

• Stream out introduction [Mentions modules, explains how sout works like a pipeline using examples]

• Standard introduction [Covers basic example of saving file locally and links to following pages]

  • Stream over HTTP
  • Stream over UDP
  • Stream over RSTP [To be started]
  • SAP session

• Transcoding introduction [Briefly explain what transcoding is, the 2x2 matrix for conversion and access=file/stream]

  • Scenario 1: No conversion + Save the file locally
  • Scenario 2: No conversion + Stream over the network
  • Scenario 3: Conversion + Save the file locally
  • Scenario 4: Conversion + Stream over the network

[I am still working on the scenario pages and hopefully I will be able to commit them tonight]

• Duplicate introduction [To be started]
• Select introduction [To be started]
• Compatibility Matrix (Table of a few of the popular codec/mux combinations, brief explanation as to which format might be preferred in which situations)

[The table is still WIP, currently I have used the old table which was made for just audio versions, I will update it after the committing the transcode scenarios].

I also have certain queries that I would like to ask:

1. Is there a difference between mux in transcode and mux in std?
2. Are there sout chains without std module? [I know that if one is streaming, they can use the http module directly instead of specifying access=http in the std block, but other than that]
3. Does UDP only support ts streams?
4. Is it possible announce/catch SAP on HTTP streaming? [No stream shows when I try with HTTP, I am not sure if it's a bug specific to my system or it happens normally].
5. If answer to 3 is yes, and to 4 is no, then does that mean there is no way to make SAP announcements for streaming ogg or matroska files?
6. SAP announcements can be made for unicast as well, right? It works when I tried although the old wiki page says otherwise.