code clean-up

I've noticed a few minor things that could do with cleaning up in the module's code:

- the code files need a @file docblock
- some functions, eg mail_logger_load(), theme_mail_logger_read_mail() are missing docblocks
- mail_logger_form_overview_submit() is incorrectly described as a hook_submit -- it's a form submission handler ;)
- missing space either side of some dot operators.
- probably other stuff if we were to run this through Coder ;)

Not much point submitting a patch when I've just filed so many others; I'll come back to this once those are in :)