✨➖📝 cli, vanth, meta, flake: Simplify dependencies, add meta crate, and improve docs

- Removed dependencies `sqlx` and `bevy_app` to simplify the project.
- Added new crate `vanth_meta` for generating example SVGs.
- Updated CLI tests to use `assert_cmd` for better test assertions.
- Enhanced README with comprehensive library and CLI usage documentation.
- Modified `Store::write` in `vanth` crate to return the content hash.
- Set `checkPhase` to empty in Nix flake configuration.

README.md

@@ -1,3 +1,89 @@
 # Vanth
 
-Vanth is a work in progress. Maybe some kind of distributed ECS database?
+Vanth is a content-addressed database as a library designed for entity-component-system (ECS) applications.
+
+It is currently experimental and should not be used for anything.
+
+## Library usage
+
+Any type that implements `serde::Serialize` can be hashed using `vanth::hash` to produce a `vanth::ContentHash`.
+
+```rust
+let x = "hello";
+assert_eq!(vanth::hash(&x).hex(), "ea8f163db38682925e4491c5e58d4bb3506ef8c14eb78a86e908c5624a67200f");
+```
+
+Derive or implement the `vanth::Vanth` trait for types you want to store in the database.
+
+```rust
+use serde::{Deserialize, Serialize};
+use vanth::Vanth;
+
+#[derive(Deserialize, Serialize, Vanth)]
+struct Data {
+    value: u32,
+}
+```
+
+This generates a method `Vanth::ty()` which returns a `vanth::Ty`. This should represent the type's fully qualified name - its module path followed by the type itself and any generics it has. E.g. `Data::<ty().to_string()` could return `my::crate::module::Data`.
+
+The derivation only works for basic types right now and is not implemented for `std` types. Moving or renaming types or modules will change the type name, necessitating a database migration. This is not supported yet.
+
+This should be used with caution. There are good reasons why `std::any::TypeId` is opaque.
+
+### Database storage
+
+```rust
+use vanth::store::{Store, StoreParams};
+
+// Or use `Store::in_memory`.
+let mut store = Store::sqlite_from_path(
+    "path/to/my_database.sqlite".into(),
+    StoreParams { create_if_not_exists: true, ..Default::default() },
+);
+let hash = store.write(Data { value: 5 }).unwrap();
+let my_data: Data = store.get_from_hash(hash).unwrap();
+```
+
+## CLI usage
+
+You can run the Vanth CLI with Nix using `nix run https://git.mascully.com/mascully/vanth`.
+
+Use `--` to pass arguments, e.g. `nix run https://git.mascully.com/mascully/vanth -- --help`.
+
+### Syntax
+
+Write a component to the database:
+
+```bash
+$ vanth write --db /path/to/db.sqlite --ty my::type::Name --value '{ "field": "value" }'
+a1cf81d8afe4e72604ea5c13bbd9b6cce14bd98c3a2f036f7156c4464a88ec09
+```
+
+Get a component from the database:
+
+```bash
+$ vanth get --db /path/to/db.sqlite --ty my::type::Name a1cf81d8afe4e72604ea5c13bbd9b6cce14bd98c3a2f036f7156c4464a88ec09
+{"field":"value"}
+```
+
+Get all components of a type from the database:
+
+```bash
+$ vanth get-all --db /path/to/db.sqlite --ty my::type::Name
+{"field":"value1"}
+{"field":"value2"}
+{"field":"value3"}
+```
+
+Delete a component by its content hash:
+
+```bash
+$ vanth delete --db /path/to/db.sqlite ea8f163db38682925e4491c5e58d4bb3506ef8c14eb78a86e908c5624a67200f
+```
+
+Delete all components of a type:
+
+```bash
+$ vanth delete-all --db /path/to/db.sqlite --ty my::type::Name
+```