Core build infrastructure

In order to ensure proper operation of the library, the core build infrastructure needs to be added & documented.

Libraries to be imported:

• capnproto (https://github.com/capnproto/capnproto)
• Botan (https://github.com/randombit/botan)
• Catch2 (https://github.com/catchorg/Catch2)

Target build systems:

• Linux (GCC)
• Linux (CLang)
• Windows (MSVC 15)

Tasks:

• Setup basic cmake build system (including directory structure)
• Add dependency lookup and fetch instructions
• Setup testing infrastructure
• Setup documentation generator
• Add CI