Split software/index.rst into multiple directories and files

[ptheywood]

The main software/index.rst is already large and growing. It may be worth splitting this into many smaller files for maintainability.

In some cases this willl seem excessive (currently) wheer pages are short on detail, but in others such as the python area this may make more sense.

It would also provide an opportunity for further organisaion. i.e. separating libraries such as boost or NCCL from languages / runtimes such as R or python, or from compiler (modules), or specific applications (suites) such as gromacs.
It may be worth attempting to mirror the module system to a certain degree for navigability. This would also allow the profiling top level to be folded into software.

I.e. as a very quick/rough mock up of a subset of the files that might need to be created :

software/
├── apps
│   ├── gromacs.rst
│   └── index.rst
├── compilers
│   ├── gcc.rst
│   ├── index.rst
│   ├── llvm.rst
│   └── nvhpc.rst
├── libraries
│   ├── HDF5.rst
│   ├── index.rst
│   └── NCCL.rst
├── tools
│   ├── CMake.rst
│   ├── index.rst
│   ├── make.rst
│   ├── nsight-compute.rst
│   └── nsight-systems.rst
└── index.rst

This will be a major conflict with any active PR's, so ideally will want doing in isolation.