Misc bugfixes from scan-build
[travis] add coverity stuff to travis
[travis] ensure we rm * last build before coverity
[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