Support for fcntl.lockf (and some minor bugfixes)

[oliver-s-lee]

See #93

[wolph]

Sorry for not responding sooner... I'm not getting all Github mails it seems... I didn't even see your previous pull request, sorry about that :(

Thank you so much for your contribution! I'm going to merge it and create a new release asap!

[wolph]

Thank you so much for the help! I'm going to create a new release today :)

[oliver-s-lee]

No problem, glad it was helpful 👍

Not sure why one of the tests wasn't passing (it was fine on mys system), but if all is green now then all good