add a seventh illusion to Optical Illusions
fix RGB primitive description
fix doc for HSB primitive
minor User Manual tweak
update FAQ to cover Android too, not just iOS
'export-world' now catches 'IllegalStateException's

Fixes #267
Merge branch '5.0.x' into topic
correct date on comments
minor cleanup in sbt build

moving stuff to a more logical place
fix performance issue with task creation (fixes #255)
Merge branch '5.0.x'

Conflicts:
	src/main/org/nlogo/nvm/ExclusiveJob.java
add some @throws annotations for the Java crowd (fixes #264)
add some @throws annotations for the Java crowd (fixes #264)
make LogoException unchecked (see #263)
fix an error handling mistake in testing

why this got uncovered by changing LogoException to not be checked,
I don't know. but it was making TestConstraintModels fail, and the
new code seems more correct to me.
get rid of old references to PMD

since we don't use it anymore
make HeadlessWorkspace.clearLastLogoException() actually work

fixes #271
Merge remote-tracking branch 'origin/5.0.x'

Conflicts:
	headless/src/main/org/nlogo/headless/HeadlessWorkspace.scala
fix recent regressions in error handling

owing to making LogoException unchecked
remove unused applet-related code