Add configuration file

[alchem0x2A]

This PR adds support for the configuration file ~/.config/ase/config.ini to include a sparc section

An example of the ini section may be

[sparc]
; `command`: full shell command (include MPI directives) to run SPARC
command = srun -n 24 path/to/sparc

; `pp_path`: directory containing pseudopotential files (optional)
pp_path = path/to/SPARC/psps

; `doc_path`: directory for SPARC LaTeX documentation to build JSON schema on the fly (optional)
doc_path = path/to/SPARC/doc/.LaTeX/

where the configurations can be used for SPARC calculator, sparc.io, and JSON API modules

@ltimmerman3 @ajmedford please take a look if the proposed keywords in sparc configure section makes sense to you

SPARC command

Equivalent to ASE_SPARC_COMMAND

command = srun -n 24 path/to/sparc 

or mix of mpi prefix and sparc binary path

sparc_exe = path/to/sparc
mpi_prefix = srun -n 24 --more-flags

The latter is more straightforward (although not cannonical ASE), and may benefit issues like #46, but I don't know if the keywords will be meaningful in the longrun

Defining custom schema

Either specify the path to LaTeX doc (equivalent to ASE_DOC_PATH)

doc_path = ~/dev_SPARC/doc/.LaTeX

or specify the path to a custom json schema

json_schema = ~/dev_SPARC/parameters.json

Psp location

Through psp_path (equivalent to SPARC_PSP_PATH)

psp_path = ~/dev_SPARC/psps

[alchem0x2A]

This is a quick implementation of #48 using the ase.config module. Although we could restructure the current logic using the newly-introduced Profile class in ASE, I personally the major migration to ASE 3.23 can be regarded as done after this PR

[ltimmerman3]

I think run_command would be clearer than command Otherwise it all looks good

[alchem0x2A]

@ltimmerman3 yeah the command argument is indeed a bit misleading but the default parameter the new FileIOCalculator looks for in the config files https://gitlab.com/ase/ase/-/blob/master/ase/calculators/calculator.py#L1145. I would say let's see how end-users' feedback will be, as long as we keep the comments in the example config files shown in the documentation