userdiff: add Elixir to supported userdiff languages

Adds support for xfuncref in Elixir[1] language which is Ruby-like
language that runs on Erlang[3] Virtual Machine (BEAM).

[1]: https://elixir-lang.org
[2]: https://www.erlang.org

Signed-off-by: Łukasz Niemier <lukasz@niemier.pl>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

userdiff.c

@@ -32,6 +32,18 @@ PATTERNS("dts",
 	 /* Property names and math operators */
 	 "[a-zA-Z0-9,._+?#-]+"
 	 "|[-+*/%&^|!~]|>>|<<|&&|\\|\\|"),
+PATTERNS("elixir",
+	 "^[ \t]*((def(macro|module|impl|protocol|p)?|test)[ \t].*)$",
+	 /* Atoms, names, and module attributes */
+	 "|[@:]?[a-zA-Z0-9@_?!]+"
+	 /* Numbers with specific base */
+	 "|[-+]?0[xob][0-9a-fA-F]+"
+	 /* Numbers */
+	 "|[-+]?[0-9][0-9_.]*([eE][-+]?[0-9_]+)?"
+	 /* Operators and atoms that represent them */
+	 "|:?(\\+\\+|--|\\.\\.|~~~|<>|\\^\\^\\^|<?\\|>|<<<?|>?>>|<<?~|~>?>|<~>|<=|>=|===?|!==?|=~|&&&?|\\|\\|\\|?|=>|<-|\\\\\\\\|->)"
+	 /* Not real operators, but should be grouped */
+	 "|:?%[A-Za-z0-9_.]\\{\\}?"),
 IPATTERN("fortran",
 	 "!^([C*]|[ \t]*!)\n"
 	 "!^[ \t]*MODULE[ \t]+PROCEDURE[ \t]\n"