doc: Add gh-pages branch as submodule in doc directory

.gitmodules

+[submodule "doc"]
+	path = doc
+	url = git@github.com:schuhschuh/gflags.git
+	branch = gh-pages

doc @ 957f0d29

+Subproject commit 957f0d291c80acbf894eb5dad918798546db9c07

doc/designstyle.css

-body {
-  background-color: #ffffff;
-  color: black;
-  margin-right: 1in;
-  margin-left: 1in;
-}
-
-
-h1, h2, h3, h4, h5, h6 {
-  color: #3366ff;
-  font-family: sans-serif;
-}
-@media print {
-  /* Darker version for printing */
-  h1, h2, h3, h4, h5, h6 {
-    color: #000080;
-    font-family: helvetica, sans-serif;
-  }
-}
-
-h1 { 
-  text-align: center;
-  font-size: 18pt;
-}
-h2 {
-  margin-left: -0.5in;
-}
-h3 {
-  margin-left: -0.25in;
-}
-h4 {
-  margin-left: -0.125in;
-}
-hr {
-  margin-left: -1in;
-}
-
-/* Definition lists: definition term bold */
-dt {
-  font-weight: bold;
-}
-
-address {
-  text-align: right;
-}
-/* Use the <code> tag for bits of code and <var> for variables and objects. */
-code,pre,samp,var {
-  color: #006000;
-}
-/* Use the <file> tag for file and directory paths and names. */
-file {
-  color: #905050;
-  font-family: monospace;
-}
-/* Use the <kbd> tag for stuff the user should type. */
-kbd {
-  color: #600000;
-}
-div.note p {
-  float: right;
-  width: 3in;
-  margin-right: 0%;
-  padding: 1px;
-  border: 2px solid #6060a0;
-  background-color: #fffff0;
-}
-
-UL.nobullets {
-  list-style-type: none;
-  list-style-image: none;
-  margin-left: -1em;
-}
-
-/*
-body:after {
-  content: "Google Confidential";
-}
-*/
-
-/* pretty printing styles.  See prettify.js */
-.str { color: #080; }
-.kwd { color: #008; }
-.com { color: #800; }
-.typ { color: #606; }
-.lit { color: #066; }
-.pun { color: #660; }
-.pln { color: #000; }
-.tag { color: #008; }
-.atn { color: #606; }
-.atv { color: #080; }
-pre.prettyprint { padding: 2px; border: 1px solid #888; }
-
-.embsrc { background: #eee; }
-
-@media print {
-  .str { color: #060; }
-  .kwd { color: #006; font-weight: bold; }
-  .com { color: #600; font-style: italic; }
-  .typ { color: #404; font-weight: bold; }
-  .lit { color: #044; }
-  .pun { color: #440; }
-  .pln { color: #000; }
-  .tag { color: #006; font-weight: bold; }
-  .atn { color: #404; }
-  .atv { color: #060; }
-}
-
-/* Table Column Headers */
-.hdr { 
-  color: #006; 
-  font-weight: bold; 
-  background-color: #dddddd; }
-.hdr2 { 
-  color: #006; 
-  background-color: #eeeeee; }
\ No newline at end of file