update urls to point to magit org
Keep the screenshot here instead of on Flickr.
Fix the logic for deciding which tag to use to build the manual.

The latest tag is the one with the *highest* number.  The ones whose names start
with letters are just noise.
Don't depend on the order in which `git tag -l` prints tag names.
Add build cruft from master to .gitignore
new version
update to v1.1.1
Update to v1.2.0
fix links
replace outdated info about contributing

(I have edited .html directly because I don't
know .tt and also could not find a build script.)
rephrase contributing notes
fix link