Support for python front- and back- ends

[rupertford]

At some point we might want to input and/or output Python. It would be useful to have a straw-person implementation to check that there are no major issues with this.

[rupertford]

Created branch 1977_python

[sergisiso]

Python offers other workflow possibilities that may be useful and we could consider:

• In the front-end, it may be the python application itself that decides what will be useful to sent to psyclone for processing and just provide the specific ast for that function/region to convert (Instead of psyclone processing the whole file and find the useful things in it). For example functions with a psyclone decorator.
• For the backend, since python has good interoperability with C FFI, it could be useful to generate the psyir with other backends e.g. Fortran with OpenACC offloading and then a Python wrapper to call that functionality.