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
It looks like this was (at least partially) implemented in
f01c86ca9b
Should fix https://github.com/fonttools/fonttools/issues/1237
I'm still not sure about that "File a bug." when AdvWidthMap is None,
but either LsbMap or RsbMap are not None..
And we still need to add tests for this though.