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-example/src/bin/simpleclient.rs

@@ -1,7 +1,7 @@
-use satrs_core::pus::verification::RequestId;
-use satrs_core::spacepackets::ecss::tc::PusTcCreator;
-use satrs_core::spacepackets::ecss::tm::PusTmReader;
-use satrs_core::{
+use satrs::pus::verification::RequestId;
+use satrs::spacepackets::ecss::tc::PusTcCreator;
+use satrs::spacepackets::ecss::tm::PusTmReader;
+use satrs::{
     spacepackets::ecss::{PusPacket, WritablePusPacket},
     spacepackets::SpHeader,
 };