Add support for interrupted versions of Good Homolosine

[TomBor]

Would be great to use this projections with mapshaper.
Information about both versions in proj website :

• https://proj.org/operations/projections/igh.html
• https://proj.org/operations/projections/igh_o.html
  Proj code :
• https://github.com/OSGeo/PROJ/blob/master/src/projections/igh.cpp
• https://github.com/OSGeo/PROJ/blob/master/src/projections/igh_o.cpp

Recent improvement in mapshaper (antimeridian and circular clipping) are really great but maybe this kind of projection involve a different way of clipping.

[mbloch]

Thanks for the links :)
I'll be working on interrupted projections soon... I'll probably put all the clipping work in the main mapshaper repo, and keep mapshaper-proj focused on transforming individual coordinates (like the PROJ library that it's based on). See: mbloch/mapshaper#483.