KaTeX website & documentation (#1484)

* website/docs: initial commit

* Change secondaryColor

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

* Fix stylesheet link

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* Change documentation link to API(Usage)

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* Add `Libraries` in usage

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

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* Use KaTeX in the parent directory to build Markdown

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* Revise function support page. Avoid error msgs.

* General edit to function support page

docs/options.md

@@ -0,0 +1,36 @@
+---
+id: options
+title: Options
+---
+You can provide an object of options as the last argument to `katex.render` and `katex.renderToString`. Available options are:
+
+- `displayMode`: `boolean`. If `true` the math will be rendered in display mode, which will put the math in display style (so `\int` and `\sum` are large, for example), and will center the math on the page on its own line. If `false` the math will be rendered in inline mode. (default: `false`)
+- `throwOnError`: `boolean`. If `true` (the default), KaTeX will throw a `ParseError` when it encounters an unsupported command or invalid LaTeX. If `false`, KaTeX will render unsupported commands as text, and render invalid LaTeX as its source code with hover text giving the error, in the color given by `errorColor`.
+- `errorColor`: `string`. A color string given in the format `"#XXX"` or `"#XXXXXX"`. This option determines the color that unsupported commands and invalid LaTeX are rendered in when `throwOnError` is set to `false`. (default: `#cc0000`)
+- `macros`: `object`. A collection of custom macros. Each macro is a property with a name like `\name` (written `"\\name"` in JavaScript) which maps to a string that describes the expansion of the macro. Single-character keys can also be included in which case the character will be redefined as the given macro (similar to TeX active characters). *This object will be modified* if the LaTeX code defines its own macros via `\gdef`, which enables consecutive calls to KaTeX to share state.
+- `colorIsTextColor`: `boolean`. If `true`, `\color` will work like LaTeX's `\textcolor`, and take two arguments (e.g., `\color{blue}{hello}`), which restores the old behavior of KaTeX (pre-0.8.0). If `false` (the default), `\color` will work like LaTeX's `\color`, and take one argument (e.g., `\color{blue}hello`).  In both cases, `\textcolor` works as in LaTeX (e.g., `\textcolor{blue}{hello}`).
+- `maxSize`: `number`. All user-specified sizes, e.g. in `\rule{500em}{500em}`, will be capped to `maxSize` ems. If set to `Infinity` (the default), users can make elements and spaces arbitrarily large.
+- `maxExpand`: `number`. Limit the number of macro expansions to the specified number, to prevent e.g. infinite macro loops. If set to `Infinity`, the macro expander will try to fully expand as in LaTeX. (default: 1000)
+- `allowedProtocols`: `string[]`. Allowed protocols in `\href`. Use `_relative` to allow relative urls, and `*` to allow all protocols. (default: `["http", "https", "mailto", "_relative"]`)
+- `strict`: `boolean` or `string` or `function` (default: `"warn"`). If `false` or `"ignore`", allow features that make writing LaTeX convenient but are not actually supported by (Xe)LaTeX (similar to MathJax). If `true` or `"error"` (LaTeX faithfulness mode), throw an error for any such transgressions. If `"warn"` (the default), warn about such behavior via `console.warn`. Provide a custom function `handler(errorCode, errorMsg, token)` to customize behavior depending on the type of transgression (summarized by the string code `errorCode` and detailed in `errorMsg`); this function can also return `"ignore"`, `"error"`, or `"warn"` to use a built-in behavior.  A list of such features and their `errorCode`s:
+  - `"unknownSymbol"`: Use of unknown Unicode symbol, which will likely also
+    lead to warnings about missing character metrics, and layouts may be
+    incorrect (especially in terms of vertical heights).
+  - `"unicodeTextInMathMode"`: Use of Unicode text characters in math mode.
+  - `"mathVsTextUnits"`: Mismatch of math vs. text commands and units/mode.
+  A second category of `errorCode`s never throw errors, but their strictness
+  affects the behavior of KaTeX:
+  - `"newLineInDisplayMode"`: Use of `\\` or `\newline` in display mode
+    (outside an array/tabular environment).  In strict mode, no line break
+    results, as in LaTeX.
+
+For example:
+
+```js
+katex.render("c = \\pm\\sqrt{a^2 + b^2}\\in\\RR", element, {
+  displayMode: true,
+  macros: {
+    "\\RR": "\\mathbb{R}"
+  }
+});
+```