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-mib/codegen/tests/verify_gen_struct.rs

@@ -1,9 +1,9 @@
-use satrs_core::res_code::ResultU16;
 use satrs_mib::res_code::ResultU16Info;
 use satrs_mib::resultcode;
+use satrs_shared::res_code::ResultU16;
 
 #[resultcode(info = "This is a test result where the first parameter is foo")]
-const TEST_RESULT: ResultU16 = ResultU16::const_new(0, 1);
+const TEST_RESULT: ResultU16 = ResultU16::new(0, 1);
 // Create named reference of auto-generated struct, which can be used by IDEs etc.
 const TEST_RESULT_EXT_REF: &ResultU16Info = &TEST_RESULT_EXT;