Pure OCaml implementation of the FAT filesystem

This library has two purposes:

1. primary: to allow the easy preparation of bootable disk images containing Mirage kernels
2. secondary: to provide a simple key=value store for Mirage applications

Note that "filesystems" are inherently legacy systems which modern Mirage applications will not use directly. The most likely use for this library is in booting a Mirage application via some kind of disk image.

Known limitations

• can only make FAT16 filesystems
• no VFAT support
• no exFAT support (see #78)
• corrupts under concurrent writes

PRs welcome to address any of these limitations!