slim down readme

the manifest section seems unnecessary to me, and it's better to
direct people to the Resources page online than to list resources here
use Markdown for readme
improve Markdown formatting of readme
improve Markdown formatting of readme
improve Markdown formatting of readme
minor readme tweaks
latest models

fixing a model that bin/release.sh was squawking about
bunch of FAQ tweaks
deprecate the applet in the User Manual
deprecate the applet in the GUI
deprecate the applet in the saved applet HTML pages
publish a test artifact too

partially addresses #561

note that for now the artifact contains only test classes, not any
test resources.  so this commit isn't as spiffy as the headless branch
equivalent in b24195a7911b90e18a3215dee42e09f9a5300310 and
214f94fddd83bf7184e3d2268058aa02f3e4990c.  it could always be further
improved later.
Merge pull request #559 from NetLogo/deprecate-applet

deprecate the applet for 5.0.6
in doc, warn more strongly against ask-concurrent
fix user manual oops
improve FAQ answer on where to find models
add a `resize-world` test
Put in note about #563
remove unneeded dummy .travis.yml

Travis now has a "only build if .travis.yml" flag that I enabled on
this repo
add an ExpressionParser test

just as a nice all-in-one example of the various AST classes