Fix highlighting for macros prefixed by "!"

Closes #201.

Checked other regexes for similar issues involving "!" and did not discover any of
significance. The Julia manual specifically calls out "!" as being special in this way and
no other symbols, so just including "!" as a special-case in regexes is sufficient.

julia-mode-tests.el

@@ -768,6 +768,13 @@ var = func(begin
     (julia--should-font-lock string 22 nil) ; =
     ))
 
+(ert-deftest julia--test-!-font-lock ()
+  (let ((string "!@macro foo()"))
+    (julia--should-font-lock string 1 nil)
+    (julia--should-font-lock string 2 'julia-macro-face)
+    (julia--should-font-lock string 7 'julia-macro-face)
+    (julia--should-font-lock string 8 nil)))
+
 ;;; Movement
 (ert-deftest julia--test-beginning-of-defun-assn-1 ()
   "Point moves to beginning of single-line assignment function."

julia-mode.el

@@ -115,6 +115,10 @@ partial match for LaTeX completion, or `nil' when not applicable."
   (let ((table (make-syntax-table)))
     (modify-syntax-entry ?_ "_" table)
     (modify-syntax-entry ?@ "_" table)
+
+    ;; "!" can be part of both operators (!=) and variable names (append!). Here, we treat
+    ;; it as being part of a variable name. Care must be taken to account for the special
+    ;; case where "!" prefixes a variable name and acts as an operator (e.g. !any(...)).
     (modify-syntax-entry ?! "_" table)
     (modify-syntax-entry ?# "< 14" table)  ; # single-line and multiline start
     (modify-syntax-entry ?= ". 23bn" table)
@@ -267,6 +271,8 @@ partial match for LaTeX completion, or `nil' when not applicable."
       ;; The function name itself
       (group (1+ (or word (syntax symbol))))))
 
+;; TODO: function definitions of form "x + y = 5" or "!x = true" not currently highlighted
+
 ;; functions of form "f(x) = nothing"
 (defconst julia-function-assignment-regex
   (rx line-start (* (or space "@inline" "@noinline")) symbol-start
@@ -302,7 +308,7 @@ partial match for LaTeX completion, or `nil' when not applicable."
   (rx "<:" (0+ space) (group (1+ (or word (syntax symbol)))) (0+ space) (or "\n" "{" "}" "end" ",")))
 
 (defconst julia-macro-regex
-  (rx symbol-start (group "@" (1+ (or word (syntax symbol))))))
+  (rx symbol-start (0+ ?!) (group "@" (1+ (or word (syntax symbol))))))
 
 (defconst julia-keyword-regex
   (regexp-opt
@@ -329,7 +335,7 @@ partial match for LaTeX completion, or `nil' when not applicable."
    ;; highlighted as a keyword.
    (list julia-quoted-symbol-regex 1 ''julia-quoted-symbol-face)
    (cons julia-keyword-regex 'font-lock-keyword-face)
-   (cons julia-macro-regex ''julia-macro-face)
+   (list julia-macro-regex 1 ''julia-macro-face)
    (cons
     (regexp-opt
      ;; constants defined in Core plus true/false