Apparently `environ` is some kind of reserved word in MSYS2's build
environment, which caused hard-to-understand linking errors on Windows
due to one of the functions in wasi.cpp having an argument named
`environ`. I've changed the name of the offending argument to `env`.
I've also added `extern "C"` to all exported functions to make sure
something like this doesn't happen again - the compiler should now
refuse to compile the code if there are function signature mismatches in
exported functions.
Right now I've implemented opening game files that are in zip format and
added a filesystem implementation to allow reading the game files. I've
also added a `Dir.glob` call core.cpp to print the contents of the root
directory of the game zip file to the log as a test.
