handle netrc not found, just return empty creds
tests for cred loading
addon-list -> addons.
Remove comment.
add maintenance commands
app features commands
rename which-app.go -> which_app.go
account features
feature-info and account-feature-info
clean error on missing API host
use ansi pkg to output must() errors in color
use ansi package for log colorization
remove unneeded LineWriter abstraction

ansi package handles turning off colors when appropriate based on the
setting made in main().
move some stuff out into util.go
improve error funcs
log.Fatalf -> printError
add printWarning() so I don't have to revisit this code when adding warning output
consistent indentation in usage examples
move more stuff into util.go
remove slug size from app list