Add bibtex and autobib support for DOIs

~~Renders DOIs using doi package in LaTeX, or emulate in HTML~~ emulates DOI package, because I couldn't figure out how to use it and get the other backends to be happy with the output.
Render URLs only if no DOI. This point is probably opinionated and perhaps should be a configuration option, but I'm not sure what the right approach is.

Rendered examples:

Example file:

meow.scrbl:

#lang scribble/acmart @nonacm @review @anonymous @screen

@(require
 scriblib/autobib
 scriblib/bibtex)

@(define-cite acite acitet generate-bibliography)
@(define-bibtex-cite* "bib.bib" acite acitet ~cite citet)

@title{Foo}

@author[
"William J. Bowman"
]

@~cite["ghuloum2006" "keep2013"]

@(generate-bibliography)

bib.bib:

@String{icfp    = {International Conference on Functional Programming ({ICFP})}}

@InProceedings{keep2013,
  author    = {Andrew W. Keep and R. Kent Dybvig},
  booktitle = icfp,
  doi       = {10.1145/2500365.2500618},
  title     = {A nanopass framework for commercial compiler development},
  year      = {2013},
  editor    = {Greg Morrisett and Tarmo Uustalu},
  pages     = {343--350},
  publisher = {{ACM}},
  bibsource = {dblp computer science bibliography, https://dblp.org},
  biburl    = {https://dblp.org/rec/bib/conf/icfp/KeepD13},
  file      = {:keep2013 - A Nanopass Framework for Commercial Compiler Development.pdf:PDF},
}

@InProceedings{ghuloum2006,
  author    = {Abdulaziz Ghuloum},
  booktitle = {Scheme Workshop},
  title     = {An Incremental Approach to Compiler Construction},
  year      = {2006},
  file      = {:ghuloum2006 - An Incremental Approach to Compiler Construction.pdf:PDF},
  keywords  = {nanopass},
  url       = {http://scheme2006.cs.uchicago.edu/11-ghuloum.pdf},
}

racket / scribble

Add bibtex and autobib support for DOIs #340