[Proj] Overhaul of docs/website/wiki and call for help

[Tom Kralidis]

All: given the wiki transition to GitHub, I think it's a good time to
dust off what's there and make things more clear.  Way forward:

1. Website

Core presence (links to docs, wiki, download, issue tracker, FAQ, etc.
This would be implemented in Markdown and leveraging GitHub pages,
which would make the web presence available at
http://osgeo.github.io/proj.4/.  If there is interest, we could
register proj4.org (maybe OSGeo could cover?), or proj4.osgeo.org.

This would either be managed a) in a gh-pages branch within
https://github.com/OSGeo/proj.4/ or b) a dedicated repo like
https://github.com/OSGeo/proj.4-www with gh-pages as the default
branch.  Note that this will also automagically update the website as
changes are made.  Pros/cons/suggestions/other options appreciated
here.

2. Documentation:

This would live in the codebase in docs/ and be made available on
https://readthedocs.org/, which would automatically generate and make
available the docs across multiple versions.  Content will be managed
by Sphinx/reStructuredText.

Table of contents:
- Introduction
- Installation
- Usage
- Testing
- Support
- Development
- License

Currently in the codebase I see:

https://github.com/OSGeo/proj.4/tree/master/html: some of these are
man pages.  How do these compare/relate to
https://github.com/OSGeo/proj.4/tree/master/man/man1 ?

https://github.com/OSGeo/proj.4/tree/master/docs/.  Looks like these
are static PDFs.  Not sure what their state is.

3. Wiki: transient/other info which does not fit into 1 or 2


Any comments, suggestions, issues would be appreciated.  Most of all,
help would be valuable with content creation/migration to rST.

Hope this helps make things easier for long term maintenance of the
"geo library everyone doesn't know they use" [1].

..Tom

[1] https://twitter.com/howardbutler/status/569577495688663040