Add `layerName` attribute to the sourcedescriptor object
Read and write layerName.
Add a source layer test.
XXX this also disables the test_check() test for the moment because it generates odd results.
When an offset refers to a table, we keep the size of the offset to
the referred-to table. When sharing tables, we were ignoring this,
which could result in a long offset being written out as a short, or
vice versa. Fix it by not sharing such tables. This is not optimal
but fixes the bug.
Bug has been there forever.
Takes a template containing predefined strings {dirname}, {basename},
{stem}, {ext} and {fullname}, to customize the location of the binary
master TTFs in relation to the designspace source filenames.
and rename getPermutations to iterAllCombinations.
It's not really permutations we are after here, but more combinations
of indexes sorted by decreasing length, from more specific to less
