First attempt at \text function

Summary:
Make all of the parsing functions keep track of whether they are
parsing in math mode or text mode. Then, add a separate lexing function to lex
text mode, which is different than the normal mode because it does weird things
with spacing and allows a different set of characters.

Test Plan:
 - See that the normal tests work
 - See that the huxley screenshot looks reasonable
 - See that none of the other huxley screenshots changed

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D7578

test/huxley/Huxleyfile

@@ -34,5 +34,8 @@ url=http://localhost:7936/test/huxley/test.html?m=\Huge{x}\LARGE{y}\normalsize{z
 [SizingBaseline]
 url=http://localhost:7936/test/huxley/test.html?m=\tiny{a+b}a+b\Huge{a+b}&pre=x&post=M
 
+[Text]
+url=http://localhost:7936/test/huxley/test.html?m=\frac{a}{b}\text{c {ab} \ e}+fg
+
 [KaTeX]
-url=http://localhost:7936/test/huxley/test.html?m=\KaTeX
+url=http://localhost:7936/test/huxley/test.html?m=\KaTeX

test/huxley/Text.huxley/record.json

@@ -0,0 +1 @@
+{"py/object": "huxley.run.Test", "screen_size": {"py/tuple": [1024, 768]}, "steps": [{"py/object": "huxley.steps.ScreenshotTestStep", "index": 0, "offset_time": 0}]}

test/katex-tests.js

@@ -447,3 +447,52 @@ describe("A sizing parser", function() {
         }).toThrow();
     });
 });
+
+describe("A text parser", function() {
+    var textExpression = "\\text{a b}";
+    var badTextExpression = "\\text{a b%}";
+    var nestedTextExpression = "\\text{a {b} \\blue{c}}";
+    var spaceTextExpression = "\\text{  a \\ }";
+
+    it("should not fail", function() {
+        expect(function() {
+            parseTree(textExpression);
+        }).not.toThrow();
+    });
+
+    it("should produce a text", function() {
+        var parse = parseTree(textExpression)[0];
+
+        expect(parse.type).toMatch("text");
+        expect(parse.value).toBeDefined();
+    });
+
+    it("should produce textords instead of mathords", function() {
+        var parse = parseTree(textExpression)[0];
+        var group = parse.value.value;
+
+        expect(group[0].type).toMatch("textord");
+    });
+
+    it("should not parse bad text", function() {
+        expect(function() {
+            parseTree(badTextExpression);
+        }).toThrow();
+    });
+
+    it("should parse nested expressions", function() {
+        expect(function() {
+            parseTree(nestedTextExpression);
+        }).not.toThrow();
+    });
+
+    it("should contract spaces", function() {
+        var parse = parseTree(spaceTextExpression)[0];
+        var group = parse.value.value;
+
+        expect(group[0].type).toMatch("spacing");
+        expect(group[1].type).toMatch("textord");
+        expect(group[2].type).toMatch("spacing");
+        expect(group[3].type).toMatch("spacing");
+    });
+});