New CLI frontend

[tomoyanonymous]

• New frontend directory was added.
• The directory contains genericapp.hpp/cpp & cli.hpp/cpp.
• genericapp.hpp contains mimium::app::GenericApp class and some option structs for compiler and runtime. This can be used for creating customizable apps in C++.
• cli.hpp contains mimium::app::cl::CliApp class. This class contains simple argument parser classes and GenericApp instance.

Now, main.cpp is implemented with this class in just one line like below.

#include "frontend/cli.hpp"
int main(int argc, char** argv) {
  return std::make_unique<mimium::app::cli::CliApp>(argc, argv)->run();
}

• Most options like --emit-ast and --emit-mir used in previous versions can be used.
• New options:
  • --backend : specifies audio driver backend. Currently, only rtaudio can be used but other choices like file & pipe will be added in the future.
  • --engine : specifies execution engine. Currently, only llvm can be used ut other choices like interpreter & wasm will be added in the future.
• CMake target mimium_llloader which can load llvm IR file exported from --emit-llvm option was removed (it was mainly used for debugging) because now we can load llvm IR(xxx.ll) files with the same CliApp class.