Add an example bib entry with multiple authors

Closes #39.

example/mu/example.bib

-% The example bibliographical entries below were borrowed from the
+% Some of the example bibliographical entries below were borrowed from the
 % <https://www.ctan.org/pkg/biblatex-iso690> package documentation.
 
+% MITTELBACH, Frank; FISCHER, Ulrike. The LATEX Companion:
+% Tools and Techniques for Computer Typesetting. 3rd ed. United States:
+% Addison-Wesley Professional, 2023. isbn 978-0138166489.
+
+@BOOK{mittelbach23,
+  author    = {Frank Mittelbach and Ulrike Fischer}, % separate multiple authors with "and"
+  date      = {2023-05-14},
+  title     = {The \LaTeX{} Companion},
+  subtitle  = {Tools and Techniques for Computer Typesetting},
+  edition   = {3},
+  location  = {United States},
+  publisher = {Addison-Wesley Professional},
+  pagetotal = {1984},
+  isbn      = {978-0138166489},
+  langid    = {english}
+}
+
 % BORGMAN, Christine L., 2003. From Gutenberg to the global information
-% infrastructure: access to information in the networked world. First. Cambridge
+% infrastructure: access to information in the networked world. 1st ed. Cambridge
 % (Mass): The MIT Press. ISBN 0-262-52345-0 [xviii, 324]
 
 @BOOK{borgman03,
-  author    = {Borgman, Christine L.},
+  author    = {Borgman, Christine L.}, % use "," to denote surname ("Borgman")
   date      = {2003},
   title     = {From Gutenberg to the global information infrastructure},
   subtitle  = {access to information in the networked world},
-  edition   = {1}, % should not be stated
+  edition   = {1},
   location  = {Cambridge (Mass)},
   publisher = {The MIT Press},
   pagetotal = {xviii, 324},
@@ -36,7 +53,7 @@
   title     = {The mirage of continuity},
   subtitle  = {reconfiguring academic information
                resources for the 21st century},
-  editor    = {Hawkins, B.L and Battin, P},
+  editor    = {Hawkins, B.L and Battin, P}, % separate multiple editors with "and"
   date      = {1998},
   location  = {Washington (D.C.)},
   publisher = {Council on Library and Information Resources;