Add support for software entry type

[k4rtik]

See https://www.softwareheritage.org/2020/05/26/citing-software-with-style/ for a well-maintained option which requires biblatex+biber

Doc: https://mirrors.mit.edu/CTAN/macros/latex/contrib/biblatex-contrib/biblatex-software/software-biblatex.pdf

[k4rtik]

If we include support for BibLaTeX, we may need to create a dedicated style as well conforming to http://biblio.eptcs.org/

[k4rtik]

Tracking issue for BibLaTeX #6