Refactor beast core, http, tests, and examples:

* Fix warnings
* Port cmake scripts to linux
* Add command line options for running test suites
* Add examples to CMakeLists
* Return std::uint64_t from writer::content_length
* basic_parser::write takes asio::const_buffer instead of pointer and size
* Turn message test back on now that it passes
* Rename to http::headers, use std::allocator, remove http_headers
* http::message::method is now a string
* Refactor to_string for ConstBufferSequence
* Remove chunk_encode from the public interface
* Initialize members for default constructed iterators
* Disallow default construction for dependent buffer sequences

Refactor http::message serialization:

* Serialization no longer creates a copy of the
  headers and modifies them
* New function prepare(), sets Connection, Transfer-Encoding,
  Content-Length based on the body attributes and caller options.
  Callers can use prepare() to have the fields set automatically,
  or they can set the fields manually.
* Use write for operator<<
* Tests for serialization

examples/file_body.hpp

@@ -0,0 +1,99 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of Beast: https://github.com/vinniefalco/Beast
+    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef BEAST_EXAMPLE_FILE_BODY_H_INCLUDED
+#define BEAST_EXAMPLE_FILE_BODY_H_INCLUDED
+
+#include <beast/http/message.hpp>
+#include <beast/http/resume_context.hpp>
+#include <boost/asio/buffer.hpp>
+#include <boost/filesystem.hpp>
+#include <cstdio>
+#include <cstdint>
+
+namespace beast {
+namespace http {
+
+struct file_body
+{
+    using value_type = std::string;
+
+    class writer
+    {
+        std::uint64_t size_;
+        std::uint64_t offset_ = 0;
+        std::string const& path_;
+        FILE* file_ = nullptr;
+        char buf_[4096];
+        std::size_t buf_len_;
+
+    public:
+        static bool constexpr is_single_pass = false;
+
+        template<bool isRequest, class Headers>
+        writer(message<isRequest, file_body, Headers> const& m) noexcept
+            : path_(m.body)
+        {
+        }
+
+        ~writer()
+        {
+            if(file_)
+                fclose(file_);
+        }
+
+        void
+        init(error_code& ec) noexcept
+        {
+            file_ = fopen(path_.c_str(), "rb");
+            if(! file_)
+                ec = boost::system::errc::make_error_code(
+                    static_cast<boost::system::errc::errc_t>(errno));
+            else
+                size_ = boost::filesystem::file_size(path_);
+        }
+
+        std::uint64_t
+        content_length() const
+        {
+            return size_;
+        }
+
+        template<class Write>
+        boost::tribool
+        operator()(resume_context&&, error_code&, Write&& write)
+        {
+            if(size_ - offset_ < sizeof(buf_))
+                buf_len_ = static_cast<std::size_t>(
+                    size_ - offset_);
+            else
+                buf_len_ = sizeof(buf_);
+            auto const nread = fread(buf_, 1, sizeof(buf_), file_);
+            (void)nread;
+            offset_ += buf_len_;
+            write(boost::asio::buffer(buf_, buf_len_));
+            return offset_ >= size_;
+        }
+    };
+};
+
+} // http
+} // beast
+
+#endif