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/release-checklist.md

@@ -0,0 +1,25 @@
+Checklist for new releases
+=======
+
+# Pre-Release
+
+1. Make sure any new modules are documented sufficiently enough and check docs with
+   `cargo +nightly doc --all-features --config 'rustdocflags=["--cfg", "doc_cfg"]' --open`.
+2. Bump version specifier in `Cargo.toml`.
+3. Update `CHANGELOG.md`: Convert `unreleased` section into version section with date and add new
+   `unreleased` section.
+4. Run `cargo test --all-features`.
+5. Run `cargo fmt` and `cargo clippy`. Check `cargo msrv` against MSRV in `Cargo.toml`.
+6. Wait for CI/CD results for EGit and Github. These also check cross-compilation for bare-metal
+   targets.
+
+# Release
+
+1. `cargo publish`
+
+# Post-Release
+
+1. Create a new annotaged tag and push it with `git tag -a satrs-core-<version>` and
+   `git push -u origin satrs-core-<version>`
+2. Create a new release on `EGit` based on the tag.
+