ServerAnnounceObserver.update() updates last_update
Extend Observers Section

Added sections for MultiplexingObserver and ServerAnnounceObserver.
Added small link to the build docs when encountering a build problem

Related to #1024
Add a minzoom option

This only affects what's written to overviewerConfig.js.  That is, it
does not change the amount of tiles rendered (it's exactly analogous to
maxzom)

Closes #994
Merge PR #1037 -- ServerAnnounceObserver.update() updates last_update
Allow --genpoi to use -c to specify a config file

Closes #1033
Added debug printout in the texture finding code
updated testrender script to re-use current python for children
Merge remote-tracking branch 'ion1/master'