Re-release of libcppa under the Boost Software License

Version 0.9.3 of libcppa has just been released ... under the Boost Software License. Since the use of LGPL-licensed code is prohibited in many companies, we have decided to re-release libcppa under a license that causes less headache in legal departments.

The user manual is available online as HTML website and as PDF document. The source code is hosted at https://github.com/Neverlord/libcppa.