renamed step backend to exchange and export iges

it can handle multiple standard exchange file formats. Changed from STEP
to IGES, because this works already.
ignore iges output directory
more common parameters
Merge branch 'master' into iges
include version file into IGES distribution
iges release
fix missing datetime
better name template for double row bearings
add iges distribution to download
fixed wrong iges dist name
added iges development snapshot
regenerated html