added PermissionError exception

specific exception for the OS permission error
returns nicer exceptions

also added "return self" for chaining
added tests for the mizfile module (SEE REMARKS)

They're not Travis compatible yet, I need someone to upload some test files

Signed-off-by: bob_boulot <bob_boulot@daribouca.net>
decreased number of tests to run

as this test-class is, at the time being, more a place-holder than anything else,
could as well reduce (drastically) the amount of time Travis (and my own
computer) has to spend on testing the function.

Signed-off-by: bob_boulot <bob_boulot@daribouca.net>
exists nicely on Keyboard interrupt

Signed-off-by: bob_boulot <bob_boulot@daribouca.net>
imports Exceptions from top level

Signed-off-by: bob_boulot <bob_boulot@daribouca.net>