we could alternatively decode these version fields as a long integer like we do elsewhere
for similar table versions, but I am not sure whether external code relies on them being
like they are now (i.e. compact decimal float).
https://github.com/fonttools/fonttools/issues/944
otherwise one gets AttributeError: 'module' object has no attribute 'block'
I noticed this by change. The whole SIL lz4-compressed Glif/Silf tables is still untested...
