`fromstep` doesn't work in reference-style links
When I try to link to a part created in a previous step using a fromstep
link, this fails in reference-style links, i.e.
Use [my printed part] in the assembly.
[my printed part]: fromstep "{note: 'this was made earlier'}"
produces a hyperlink to fromstep
and doesn't sub in the part, without any warnings.
Use [my printed part](fromstep)
appears to work OK.