A number of additions and changes

[mlo-poc]

I know, it is discouraged to do this.
I started using GradeMan a few years ago and bit by bit I changed it to fit my needs.

1. added an markdown parser for notes
2. ported the code to python3
3. changed the grade-calculation logic
4. made some minor adjustments I don't really recall

[polarwinkel]

actually you are encouraged to to this!
Thanks a lot for your changes!
Since I am using my new GradeMan2 I didn't find time to port this to python3, so people are contacting me having issues with newer ubuntu- und debian-versions.
Ad there remain still good reasons to stay with this version, since GradeMan2 is much more designed to be used as your personal cloud server, requiring more knowledge to set it up.

So I'll be glad to have a look at your changes the next days and merge them if all is fine.

[polarwinkel]

I just cherry-picked the python3-port and made a new release from that.
I might take a look in your grade-calculation logic some day, but since the pull-request mixes up all your changes its a little more handwork to do.

I saw you forked my GradeMan2 as well, feel free to send pull-requests for that as well! It just would make things a little easier if you could make one request for one certain change.
For example my grade-calculation logic isn't implemented yet ;-)
(I don't use grade calculations and do final grades the pedagogical way, but it's the most asked-for feature, so I planned to implement it and have preparations for that)