Fix bug with error not being written to stderr

Fix lint warning

Only the usage message was written to stderr, the error was written with
the standard fmt.Println.

Write usage message to stderr on error

Remove excess trailing whitespace from Usage generation

When the parsing of parameters/flags fails eg. when a required flag is
missing, print the usage statement and error to stderr instead of
stdout.

Add coveralls badge

Add more tests for parser

add tests for usage info

add coveralls to .travis.yml