More updates to 0.92 Release Notes (still incomplete)
Add release notes to Help section

Improve build.xml to convert CURRENT-RELEASE.ml into HTML using
pandoc(1).  For alpha, beta and release builds, if pandoc(1) is not
installed, fail the build

Simplify the main Help screen to a list of descriptive links (not labels
with captions) and add a link to releasenotes.html