Add docs/README.txt
Add Sphinx docs
Add to .gitignore
Add sphinx13 theme
Move images to new docs folder
update sphinx docs layout
delete html documentation
Move latex documentation to docs
update sphinx docs
Add gammalib favicon
Remove gammalib header image (no longer needed, done as text)
Update Sphinx docs layout to show banner (logo and text)
Convert gammalib_um to RST format

I used pandoc and then did quite a bit of hand-editing.
Convert Coding and Design Conventions CDC from latex to rst
rename docs folder back to doc
Output now goes into build/doxygen
Add sphinx and doc rule for sphinx code building and Doxygen + sphinx code building.
Ignore doc/build directory.
Merge branch 'docs2' into integration