[api-minor] Change getOutline to actually return the RGB color of outline items

Currently the `C` entry in an outline item is returned as is, which is neither particularly useful nor what the API documentation claims.

This patch also adds unit-tests for both the color handling, and the `F` entry (bold/italic flags).

src/display/api.js

@@ -721,7 +721,7 @@ var PDFDocumentProxy = (function PDFDocumentProxyClosure() {
      *   title: string,
      *   bold: boolean,
      *   italic: boolean,
-     *   color: rgb array,
+     *   color: rgb Uint8Array,
      *   dest: dest obj,
      *   url: string,
      *   items: array of more items like this