added --use-vpb argument
fgelev: added --tile-file argument
fgelev: enable VPBActive via SGSceneFeatures() as well
When fgelev runs, it does not load the scenery through the normal
process of FGScenery::ScenerySwitchListener(), so
SGSceneFeatures::instance()->setVPBActive() won't get called
unless we do it manually here.
Add man pages for those programs that did not have one (exceptions:
yasim and yasim-proptest) and update the existing ones to make them
compliant with man-pages(7) conventions.