Add memory specification to file

[lilyminium]

Description

Relates to #168 , #169

This sets the memory usage in the input file. The other way is to use commandline (psi4 --memory), which I decided not to go with because:

• it's more difficult to test
• it makes it easier to theoretically pass around input files as the memory requirements are encoded

[mattwthompson]

LGTM - I don't feel strongly about encoding a memory limit in the file or passing it to the command, but the existing design seems to put as much as possible in the input file, so sticking with that seems good

@sef43 do you think this will solve your issue? AFAICT, all that's needed is passing in the "memory 2 GB" line into the file and this PR seems to do just that

[mattwthompson]

Teensiest nit (which can be passed on): future me would benefit from dropping in this link to know why this default value was used

https://psicode.org/psi4manual/master/psithoninput.html#memory-specification

[lilyminium]

Thanks for the review Matt -- added!

[sef43]

@sef43 do you think this will solve your issue? AFAICT, all that's needed is passing in the "memory 2 GB" line into the file and this PR seems to do just that

Yes this works, thanks