add feature toggles to gitoxide (CLI) itself

This allows to go for minimal size or for maximum performance.

Cargo.toml

@@ -13,9 +13,13 @@ path="src/main.rs"
 test = false
 doctest = false
 
+[features]
+default = ["fast"]
+fast = ["git-features/parallel", "git-features/fast-sha1"]
+
 [dependencies]
 gitoxide-core = { version = "0.1.0", path = "gitoxide-core" }
-git-features = { version = "0.1.0", path = "git-features", features = ["parallel", "fast-sha1"] }
+git-features = { version = "0.1.0", path = "git-features" }
 anyhow = "1.0.31"
 structopt = "0.3.14"
 

Makefile

@@ -33,10 +33,7 @@ tests: check unit-tests journey-tests ## run all tests, including journey tests
 
 check: ## Build all code in suitable configurations
 	cargo check --all
-	cd git-odb && cargo check --no-default-features --features fast-sha1 \
-			   && cargo check --no-default-features \
-			   && cargo check --all-features
-	cd git-features && && cargo check --all-features \
+	cd git-features && cargo check --all-features \
 			   && cargo check --features parallel \
 			   && cargo check --features fast-sha1
 

README.md

@@ -147,7 +147,22 @@ Provide a CLI to for the most basic user journey:
 * [ ] add a remote
 * [ ] push
 
-### `git-features` guide
+## Cargo features guide
+
+Cargo uses feature toggles to control which dependencies are pulled in, allowing users to specialize crates to fit their usage.
+Ideally, these should be additive.
+This guide documents which features are available for each of the crates provided here and how they function.
+
+### gitoxide
+
+The top-level command-line interface.
+
+* **fast** (default)
+  * Makes the crate execute as fast as possible by supporting parallel computation of otherwise long-running functions
+    as well as fast, hardware accelerated hashing.
+  * If disabled, the binary will be visibly smaller.
+
+### git-features
 
 A crate to help controlling which capabilities are available from the top-level crate that uses `gitoxide`.
 All feature toggles are additive.