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) In general, people are not editing gnuradios documentation, so perhaps we need to make it even easier to edit?
 * 3) 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
 * 4) 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.
 * 5) 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.
 * 6) 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).
 * 7) The wiki itself needs a re-org, or at least a minor clean up.  Perhaps categorize pages into documentation/tutorials/news/events/archives
 * 8) The python manual contains almost no useful info.  If its only purpose is going to be a list of python version's of functions, blocks, then there is probably a better way to present that info

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