Refactor sources to make easier to compile with other build systems

[edubart]

Context

People may want to bundle libcartesi in other projects and may need to use other build systems, the problem is that we have some generated files that can only be generated in our Makefile build system. We should refactor our sources in a way that at least libcartesi is easy to build with other build tools (e.g CMake, node-gyp, etc).

Subtasks

• Make machine-c-version.h available in the source tarball.
• Create an include directory in src, to make easy to just copy include headers.
• Simplify and make some defines non mandatory to make more difficult to do mistakes when compiling with other build systems
• Provide a small CMakeLists.txt project (optional to use and focusing on libcartesi only)