[plugin system] Add defineSymbol to the main katex object (#1263)

* Expose defineSymbol in the main KaTeX object

* More Unicode letters (#1260)

This PR serves as a complement to PR #1232 by supporting some letters that are omitted from the Unicode range 1D400–1D7FF.

* Include Bold-Italic fonts for \boldsymbol (#1257)

* Include Bold-Italic fonts for \boldsymbol

Fix #1228

* Update screenshots

* README: Add size badge (#1253)

* README: Add size badge

Add a size badge showing size of gzipped katex.min.js

* update-sri: Add code to replace size badge in readme

* Change to use badge from shields.io instead

My bad for assuming that badgesize.io supports https. Change to use the
badge from shields.io which supports https.

* More Unicode letters (#1260)

This PR serves as a complement to PR #1232 by supporting some letters that are omitted from the Unicode range 1D400–1D7FF.

* Include Bold-Italic fonts for \boldsymbol (#1257)

* Include Bold-Italic fonts for \boldsymbol

Fix #1228

* Update screenshots

* README: Add size badge

Add a size badge showing size of gzipped katex.min.js

* update-sri: Add code to replace size badge in readme

* Change to use badge from shields.io instead

My bad for assuming that badgesize.io supports https. Change to use the
badge from shields.io which supports https.

* Use badgesize.io with https

* Fix space width in \texttt (#1261)

* Fix space width in \texttt

Fix #1255 via https://github.com/KaTeX/katex-fonts/pull/41.
Also fix width metrics via https://github.com/KaTeX/katex-fonts/pull/42.

* Improve test

* Update screenshots

katex.js

@@ -18,6 +18,8 @@ import utils from "./src/utils";
 import type {SettingsOptions} from "./src/Settings";
 import type ParseNode from "./src/ParseNode";
 
+import { defineSymbol } from './src/symbols';
+
 /**
  * Parse and build an expression, and place that expression in the DOM node
  * given.
@@ -68,7 +70,6 @@ const generateParseTree = function(
     return parseTree(expression, settings);
 };
 
-
 /**
  * Generates and returns the katex build tree. This is used for advanced
  * use cases (like rendering to custom output).
@@ -137,4 +138,8 @@ export default {
      * to change. Use at your own risk.
      */
     __renderToHTMLTree: renderToHTMLTree,
+    /**
+     * adds a new symbol to internal symbols table
+    */
+    __defineSymbol: defineSymbol,
 };