Minor improvements

[hrueger]

Hi @ybouane,
thanks for this very cool library! I'm working on a Camera Characterization Tool for University and this perfectly fits for loading the raw files 🎉

I did have some improvements, feel free to pick what you like:

• added a rawImageData function to get raw, undebayered sensor data (sorry for the typo in the commit message)
• the build process now uses submodules instead of cloning the repo, because that makes it easier to have a fixed version of libraw lib and improves the build speed
• I refactored the directory structure to clean it up a bit
• I added typescript support
• I fixed the example (some cors headers adre needed for the SharedArrayBuffer to be available (at least in my testing)
• I gitignored dist files

I should still add some docs to the readme about the changes in the build process, I think, like initing submodules with git submodule update --init