Reduce kernel heap to 64 MB
Fix issue in build.rs

There was a bug at the `initfs` generation which made the listing of the contents of the `initfs:`subdirectories impossible from the command line.

The subdirectory listing data had the full paths of the files (like `bin/ahcid\nbin/bgad\n...`) when it should just only be the names of the files (`ahcid\nbgad\n...`)

initfs folder should be specified in INITFS_FOLDER environment variable
As a result kernel module can be compiled on it's own.