Get `run_key_action` to export correctly to C

Add a new wrapper function for `run_key_action` that uses C appropriate
inputs & outputs and calls into our Rusty `run_key_action`. This new
function now correctly gets a header generated for it by 'cbindgen'.

Immense thanks to Jake Goulding on the Rust FFI Omnibus for showing me
how to pass a slice argument from C:
http://jakegoulding.com/rust-ffi-omnibus/slice_arguments/

In order to pass the slice from C, we need to pass a C array and its
length to the function. Cool.

1 files changed, 2 insertions, 0 deletions

diff --git a/dome_key_map.h b/dome_key_map.h
index 473d2f0..d128979 100644
--- a/dome_key_map.h
+++ b/dome_key_map.h
@@ -20,3 +20,5 @@ typedef struct {
   Option_CString action;
   MapKind kind;
 } KeyActionResult;
+
+const KeyActionResult *c_run_key_action(const HeadphoneButton *trigger, size_t length);