Cardano Updates

+  set biber to use a style similar to `abbrv` (which isn't available in biblatex)
+  add cleverref and change (hopefully all) occurrences of `\ref` to one of
   `\Cref` or `\cref` or `\crefrange`.
+  move agda-specific macros to `agda-latex-macros.sty`
+  improve organization of, and comments in, `preamble.tex` file
+  add macro `\hrefAgdaWiki` to help enforce more consistent refs to Agda
+  append `{}` to end of some uses of latex macros, and remove `\xspace`
   from definition of those macros (todo: do this for all `\xspace`s)
+  add title page, list of contributors, and date

+ move EssentialAgda module outside Ledger module
+ add new macro for referencing official Agda docs
+ uncomment paragraph that may have been deleted accidentally;
  (remove it later if it was deleted on purpose)