Rework block navigation to improve handling of interstitial comments
Rework block navigation to improve handling of interstitial comments

Fixes GH-88.

Reported-By: da39a3ee5e6b4b0d3255bfef95601890afd80709@parno.

FStarLang/fstar-mode.el,FStarLang/fstar-mode.el,FStarLang/fstar-mode.el