removed "runtests.R" file

File should have been removed after rename to unitizer, but somehow was
not.
removed legacy `U` browse option
in Review, omit sect titles when only one section
change prompt text for Review
updated Help message in Review
follow up from removing "runtests.R"
Fixes to navigation

Typing in number was not going to correct test.
Fixes to quitting logic

* Quitting did not work properly from Review menu
* N now also a valid response to final prompt
Further work on "vignette"
doc updates