Cargo packages were updated to their latest versions. The integration
test in .gitlab-ci.yml was rewritten to handle the latest iteration of
the kernel, where it'll just loop forever if it's not killed.

Comments were added everywhere. This should make the code a bit easier
to read. Some old, commented-out code was removed as well. The use
statements were cleaned up a little bit, I had to duplicate all uses of
Vec and VecDeque to make both the kernel and tests happy but that has
been cleaned up.

Labels from seL4 were added. This means that our invocation labels will
be compatible with seL4. Some of the error types were also grouped up
into a unifying error type, now located in src/error.rs.

The userspace program now prints a friendly message, created with
figlet :)