restructure the crate

- 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/tcp.rs

@@ -4,7 +4,7 @@ use std::{
 };
 
 use log::{info, warn};
-use satrs_core::{
+use satrs::{
     hal::std::tcp_server::{ServerConfig, TcpSpacepacketsServer},
     spacepackets::PacketId,
     tmtc::{CcsdsDistributor, CcsdsError, TmPacketSourceCore},