updates websocketpp::exception to wrap lib::error_code
switch all exceptions to be of type websocketpp::exception
remove dependency on std::iostream from core

It is still required for the iostream transport and the basic
(iostream) logging policy.
Adds a stub transport policy

This will be used in the minimal config to avoid bringing in iostream
dependencies. It will also be used to document the minimal interface
for writing a custom transport policy.
Add minimal_client and minimal_server configs references #338
remove references to unused iostream header from asio transport
added a note about breaking changes in the logging policy API
Merge branch 'master' into core_dependencies

Conflicts:
	changelog.md
update changelog
Merge branch 'master' into exception_refactor
Disable open timeout when duration is set to zero
package for 0.3.0 release
Reduce conflict between std::min and macros

Adjust usage of std::min to be more compatible with systems that define
a min(...) macro
update version information for develop branch
Merge branch 'exception_refactor' into develop

Conflicts:
	changelog.md
	websocketpp/impl/connection_impl.hpp
make version introduced notes less specific
Merge core requirements feature branch
Recommend do not override CMAKE_INSTALL_PREFIX on MSVC

I'm a Windows user, I don't actually want this--I can set CMAKE_INSTALL_PREFIX myself if necessary.  When I install websocketpp, I intend for the installation to be to a place that's similar in sense to what it is on Unix systems, which on Windows is generally Program Files.  By allowing the CMAKE_INSTALL_PREFIX path to simply default, not only does this default behavior automatically appear, but it also corrects a problem currently existing with the INSTALL project which causes the websocketpp-config.cmake installed by the INSTALL project to contain invalid entries.