libiou: add libiou submodule

libiou is a thin veneer over io_uring defining an ergonomic async
IO-oriented API.

Since jio shouldn't need to do anything computationally
intensive, the combination of thunk_h for closures and
libiou+io_uring for scheduling closures according to IO
completions should be sufficient for an implementation.  Though
it may prove annoying to not have per-task stacks and the ability
to arbitrarily yield and/or delay execution pending completion of
non-IO results, we'll see.

1 files changed, 0 insertions, 0 deletions

diff --git a/libiou b/libiou
new file mode 160000
+Subproject c7d7e01bf5da362c4a8065efedc6dc7836471f6