Implement `nimbus build` command for project build

[kfejzic]

Implement the nimbus build command to streamline the build of the previously initialized C++ projects using the nimbus build system. This command should(at this stage):

• In case of first run, create a build/ dir, starting the build process of all .cpp and .c files in the projects src/ directory and all it's subdirectories recursively, generating an executable with the projects name, utilizing the nimbus.toml configuration (compiler, standard, build mode).
• In case of each following run, perform an incremental build, rebuilding touched files, generating an executable with the projects name, utilizing the nimbus.toml configuration (compiler, standard, build mode).