Allows install paths with spaces on MacOS

[TimArt]

I've modified the MacOS build script to allow compilation in a directory hierarchy that includes directory names with spaces in them. I did this by using "weak quoting" in bash. I also added git submodule initialization and updating so when a user goes to build for MacOS they do not first need to know about git submoduling.

I've added a comment on each line I've changed to help explain. Some of these comments are unnecessary and will probably be removed.

Thanks!

[thp]

Yeah, no need to add comments to each line. Remove the comments if possible. Also, maybe this is a good time to run it through the shellcheck utility (https://www.shellcheck.net, brew install shellcheck on macOS) and fix those things.

[TimArt]

I removed my unnecessary comments and corrected the following lines based on shellcheck:

Let me know if there's anything I've done that you want modified.

[thp]

Cool, thank you!