KaTeX website & documentation (#1484)

* website/docs: initial commit

* Change secondaryColor

* Fix index.css not being copied and included on global stylesheet

* Fix stylesheet link

[skip ci]

* Change documentation link to API(Usage)

[skip ci]

* Add `Libraries` in usage

[skip ci]

* Remove documentation from `README.md` and add link to the site

[skip ci]

* Use KaTeX in the parent directory to build Markdown

[skip ci]

* Revise function support page. Avoid error msgs.

* General edit to function support page

website/package.json

@@ -0,0 +1,14 @@
+{
+  "scripts": {
+    "start": "docusaurus-start",
+    "build": "docusaurus-build",
+    "publish-gh-pages": "docusaurus-publish",
+    "write-translations": "docusaurus-write-translations",
+    "version": "docusaurus-version",
+    "rename-version": "docusaurus-rename-version"
+  },
+  "devDependencies": {
+    "docusaurus": "^1.3.2"
+  },
+  "dependencies": {}
+}