Support for \' \` \^ \~ \= \u \. \" \r \H \v text-mode accents (#802)

* Support for \' \` \^ \~ \= \u \. \" \r \H \v text-mode accents

* bug fix

* Possible Safari fix

* Forbid text accents in math mode

* Switch to noncombining characters for most accents. Revert Safari change.

* Add tests

* Found non-combining diaresis accent too

test/errors-spec.js

@@ -140,6 +140,11 @@ describe("Parser:", function() {
                 "Can't use function '\\sqrt' in text mode" +
                 " at position 7: \\text{\\̲s̲q̲r̲t̲2 is irrational…");
         });
+        it("rejects text-mode-only functions in math mode", function() {
+            expect("\\'echec").toFailWithParseError(
+                "Can't use function '\\'' in math mode" +
+                " at position 1: \\̲'̲echec");
+        });
     });
 
     describe("#parseArguments", function() {