Adds asio library and Storage Module

lib/asio-1.18.0/doc/asio/overview/cpp2011/futures.html

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+<div class="titlepage"><div><div><h4 class="title">
+<a name="asio.overview.cpp2011.futures"></a><a class="link" href="futures.html" title="Futures">Futures</a>
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+<p>
+          The <code class="computeroutput">asio::use_future</code> special value provides first-class support
+          for returning a C++11 <code class="computeroutput">std::future</code> from an asynchronous operation's
+          initiating function.
+        </p>
+<p>
+          To use <code class="computeroutput">asio::use_future</code>, pass it to an asynchronous operation
+          instead of a normal completion handler. For example:
+        </p>
+<pre class="programlisting">std::future&lt;std::size_t&gt; length =
+  my_socket.async_read_some(my_buffer, asio::use_future);
+</pre>
+<p>
+          Where a handler signature has the form:
+        </p>
+<pre class="programlisting">void handler(asio::error_code ec, result_type result);
+</pre>
+<p>
+          the initiating function returns a <code class="computeroutput">std::future</code> templated on
+          <code class="computeroutput">result_type</code>. In the above example, this is <code class="computeroutput">std::size_t</code>.
+          If the asynchronous operation fails, the <code class="computeroutput">error_code</code> is converted
+          into a <code class="computeroutput">system_error</code> exception and passed back to the caller
+          through the future.
+        </p>
+<p>
+          Where a handler signature has the form:
+        </p>
+<pre class="programlisting">void handler(asio::error_code ec);
+</pre>
+<p>
+          the initiating function returns <code class="computeroutput">std::future&lt;void&gt;</code>. As
+          above, an error is passed back in the future as a <code class="computeroutput">system_error</code>
+          exception.
+        </p>
+<p>
+          <a class="link" href="../../reference/use_future.html" title="use_future">use_future</a>, <a class="link" href="../../reference/use_future_t.html" title="use_future_t">use_future_t</a>,
+          <a class="link" href="../../examples/cpp11_examples.html#asio.examples.cpp11_examples.futures">Futures example (C++11)</a>.
+        </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M.
+      Kohlhoff<p>
+        Distributed under the Boost Software License, Version 1.0. (See accompanying
+        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+      </p>
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