generalize workchain sphinx extension to processes

[ltalirz]

Fixes #3016

This PR

• generalizes the "workchain" sphinx autodoc extension
• uses it to replace documentation of the CalcJob interface

I.e. you can now do:

.. aiida-process:: CalcJob
    :module: aiida.engine.processes.calcjobs

.. aiida-calcjob:: CalcJob
    :module: aiida.engine.processes.calcjobs

.. aiida-workchain:: WorkChain
    :module: aiida.engine.processes.workchains

Currently, the implementation of the aiida-workchain and aiida-calcjob directives are identical to aiida-process (simply inherit from the class) but they can easily be customized in the future.

This PR includes some modifications introduced by #3299

[ltalirz]

Closing for further updates & harmonization with #3299

[ltalirz]

@sphuber ready for review now :-)

[sphuber]

Thanks a lot @ltalirz

[ltalirz]

Hm... while the docs build on travis seems to work fine, it seems this broke the docs build on readthedocs.

Espen mentioned something like this as well but I may have misunderstood him before.
We'll need to look into this.

[d-tomerini]

Hi @italirz,

as I mentioned, just a typo at line 468 of your new version (dimnensional) in the page.

For the mpirun_extra_params I'd specify that the mpi run command is defined in the :ref:computer setup<computer_setup> section, for anyone interested, for the resources section I'd refer to the scheduler manual page to access the options. For the rest, the help does its job.

Also, I'd clearly state always when the value to be supplied is not a string (Boolean or AiiDA object)

[sphuber]

Also, I'd clearly states always when the value to be supplied is not a string (Boolean or AiiDA object)

For that we should use the valid_type keyword in the spec. If this is currently not used for some CalcJob options, we should add them. This keyword is automatically parsed by the Sphinx extenstion