Documentation re-org 2018

Issues to work out as part of this re-org

1. Usage manual may be hard to find for new people, and has been getting almost zero updates/refinements
2. Should we just move the usage manual to the wiki so that the doxygen manual is only block-specific stuff? What about people who need to work offline? see Exporting Usage Manual
3. When you go to https://gnuradio.org/doc/doxygen/ the organization may be confusing for new people, and several of the drop downs don't have useful info. The wiki home page attempts to provide guidance.
4. We don't define what type of information goes where. E.g., if someone new-ish wants to get more info about something (e.g. PMTs), it's not clear whether to use the wiki or usage manual.
5. Some information is duplicated across the wiki and usage manual (e.g. the wiki's BlocksCodingGuide is like a condensed version of several usage manaul sections).
6. The wiki itself needs a re-org, or at least a minor clean up. Perhaps categorize pages into documentation/tutorials/news/events/archives

Current State

GNU Radio documentation lives in one of the following places:

1. Usage Manual in Doxygen (18 pages that cover various topics across GR)
2. "Components" descriptions in Doxygen (various length blurbs about each category of GNU Radio blocks)
3. Doxygen strings for each block, describing arguments and such (this info lives in the same files as the code for the block)
4. Python (Sphinx) manual here, not much in it though
5. Wiki

Big Question

Whether we want to use doxygen or the wiki for the non-block-specific documentation

Arguments for using the wiki:

1. We have a wiki, non-veteran people may assume that it is the primary source for how-to's and such
2. Wiki has more tools suited for this type of non-block-specific documentation
3. Quicker to make a change, changes immediately show up (changes to the doxygen require a git fork/PR and don't show up for months)
4. Searching (through Google or the wiki itself) works a little better than searching for something in doxygen

Arguments for using doxygen:

1. You can click functions/blocks/class names and it links to the corresponding page of the API
2. People using an older version of GNU Radio can get the corresponding older version of the usage manual (argument countered if we use Exporting Usage Manual)
3. Changes are through git so they are very much backed up, backing up the wiki is more manual

Notes on Usage Manual Conversion

1. Build Instructions and Information -I went through and copied info that didn't exist elsewhere to BuildGuide
2. Exploring GNU Radio -contains two tutorials that are super short and don't add anything more to what is already in the guided tutorials
3. Handling flow graphs -CONVERTED
4. Polymorphic Types -CONVERTED
5. Metadata Information -CONVERTED
6. Message Passing -CONVERTED
7. Stream Tags -CONVERTED
8. Tagged Stream Blocks -CONVERTED
9. Logging -CONVERTED
10. Performance Counters -CONVERTED
11. Block Thread Affinity and Priority -CONVERTED
12. Configuration files -CONVERTED
13. Python Blocks -I folded the material into the other manual sections (wiki version only)
14. Polyphase Filterbanks -extracted info into a new manual page on using PFBs
15. OFDM -converted it to wiki and now its listed under tutorials
16. Packet Data Transmission -essentially a tutorial on how to use an obscure set of blocks, not sure if its even worth carrying over
17. Out-of-Tree Configuration -everything here is covered in the OutOfTreeModules page, granted that page needs to be organized
18. Instructions for using VOLK in GNU Radio -CONVERTED