Simplex is broken

[LourensVeen]

Describe the bug
Simplex doesn't compile.

This code has multiple issues:

• It includes a copy of HEALpix that is so obsolete it doesn't compile anymore
• It includes a copy of QHull that doesn't compile with clang
• It includes a copy of HDF5 that doesn't compile with clang
• It has obsolete source code itself and doesn't compile

The dependencies are all commonly available, so they should just be installed using a package manager, which will also keep them up to date. Simplex itself may need updates to work with newer versions of these, and the whole thing needs to be made to work with both gcc and clang.