reorganize into separate crates

- taskchampion -- core implementation of a replica
 - taskchampion-cli -- command-line interface
 - taskchampion-sync-server -- server implementation (not much yet!)

taskchampion/docs/src/SUMMARY.md

@@ -0,0 +1,11 @@
+# Summary
+
+- [Installation](./installation.md)
+- [Usage](./usage.md)
+---
+- [Data Model](./data-model.md)
+  - [Replica Storage](./storage.md)
+  - [Task Database](./taskdb.md)
+  - [Tasks](./tasks.md)
+- [Synchronization](./sync.md)
+  - [Planned Functionality](./plans.md)