Korektor 2.0.0

Changes against previous release:

• Move to github.
• Start using Semantic Versioning http://semver.org/.
• Use C++ BuilTem http://github.com/ufal/cpp_builtem as build system.
• Use t2t_docsys http://github.com/ufal/t2t_docsys as documentation system.
• Use microrestd http://github.com/ufal/microrestd as REST server.
• Provide new korektor binary with many options and also a REST service.
• Support Linux (gcc, clang), Windows (tdm-gcc, Visual C++), OS X (clang).