Re-structure sat-rs

- Add new shared subcrate satrs-shared to split off some shared
  components not expected to change very often.
- Renmame `satrs-core` to `satrs`. It is expected that sat-rs will remain
  the primary crate, so the core information is superfluous, and core also
  implies stability, which will not be the case for some time.

satrs/src/hk.rs

@@ -0,0 +1,16 @@
+pub type CollectionIntervalFactor = u32;
+pub type UniqueId = u32;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum HkRequest {
+    OneShot(UniqueId),
+    Enable(UniqueId),
+    Disable(UniqueId),
+    ModifyCollectionInterval(UniqueId, CollectionIntervalFactor),
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub struct TargetedHkRequest {
+    target: u32,
+    hk_request: HkRequest,
+}