Improve I/O traits and wrapper types, add support for FAT filesystems (#407)

* Use delegation to forward I/O trait implementations through our various I/O structs, a better approach than using Deref/DerefMut since it allows easy chaining of types that must implement an I/O trait.

* Use our own fork of `fatfs` which allows us to set the logging level.

* Includes simple proof of concept for interfacing with a FAT32 filesystem, which is commented out by default. 0f27e797e65640d4e44ed3cd5d392a50d2b07cee