Implement (rendering of) German tablature

Some issues specific to German tablature:

Beaming of smaller-value rhythm flags into what Newsidler in the introduction to his 1536 book calls Leiterlein (ladders). Although this feature is not unique to German tablature, it is done very consistently there (maybe even without exception? - I'm not sure). Marc Lewon noted, in another discussion, that they "group certain gestures in a suggestive way, which we should not lose in our transliteration."
There are multiple ways to refer to the frets on the sixth course. Marc Lewon suggests to start with the four mentioned in Newsidler 1536, which he considers to be the most important ones:
The relative vertical position of the symbols; we should have flexibility in placement. There are four options:
- all the symbols are squished together as closely as possible so that they always align at the top (or bottom?) - see the Gerle example below;
- the symbols are organised in polyphonic lines; this is more rare - see the Ochsenkun example below (note that some symbols are doubled as to indicate unisons);
- a mix of both - see the Newsidler example below;
- (in manuscripts) in cases where the scribe forgot a symbol, it is added below the others, leading to some sort of reversal/interruption of the 'logical' (i.e., from low to high) sequence of the symbols.

Examples:

gerle-1552_1-no_4.png

ochsenkun-1558_5-no_31.png

newsidler-1536_7-no_11.png

music-encoding / tablature-ig