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/lib.rs

@@ -1,8 +1,8 @@
 use derive_new::new;
-use satrs_core::spacepackets::ecss::tc::IsPusTelecommand;
-use satrs_core::spacepackets::ecss::PusPacket;
-use satrs_core::spacepackets::{ByteConversionError, CcsdsPacket};
-use satrs_core::tmtc::TargetId;
+use satrs::spacepackets::ecss::tc::IsPusTelecommand;
+use satrs::spacepackets::ecss::PusPacket;
+use satrs::spacepackets::{ByteConversionError, CcsdsPacket};
+use satrs::tmtc::TargetId;
 use std::fmt;
 use thiserror::Error;