[axe.c] fix all coverity bugs

Mostly resource leaks on rare error conditions
[README] add coverity badge
Fix more errors after code review
[main.c] fix copypaste error in cli parsing
[libaxe] fix retval = -1 in load_tries

load_tries_single always returned -1, even on success. This fixes that
[travis] fix global env vars in travis
[travis] try fixing coverity env var syntax
[README] add coveralls badge
[travis] more attempts to fix travis ci
[travis] seperate env global section for coverity
[travis] rtfm! this should fix coverity + travis