Implement \verb (#614)

* Implement \verb

* Implement @gagern's comments

* \verb: look up characters one at a time.

* Add screenshot test for \verb

* Add error tests for \verb

* Include space symbol in typewriter font, and fix single quotes

This is based on https://github.com/Khan/MathJax-dev/pull/2
which hasn't been accepted yet at the time this commit is made.

* Add \verb* tests

* \verb should use Typewriter-Regular font!

* Switch \verb to use text mode and no-break space.

* Screenshot update with Typewriter-Regular

* \verb test: fix *, add commas to make spaces clear

* Fix spaces and style handling

* Implement @kevinbarabash's comments

* Make error clearly an assertion failure

* verb screenshot for Chrome

test/errors-spec.js

@@ -183,6 +183,17 @@ describe("Parser:", function() {
         });
     });
 
+    describe("#verb", function() {
+        it("complains about mismatched \\verb with end of string", function() {
+            expect("\\verb|hello").toFailWithParseError(
+                "\\verb ended by end of line instead of matching delimiter");
+        });
+        it("complains about mismatched \\verb with end of line", function() {
+            expect("\\verb|hello\nworld|").toFailWithParseError(
+                "\\verb ended by end of line instead of matching delimiter");
+        });
+    });
+
 });
 
 describe("Parser.expect calls:", function() {