SLT index

[pyRis]

Create also these new indices (probably automatic ones):

auto-slt-en2cs (*.en.OS.ogg -> .cs.OSt)
auto-slt-cs2en (.cs.OS.ogg -> *.en.OSt)
These new indices should include also other documents which allow this type of evaluation, e.g. auto-slt-en2cs should include antrecorp etc.