Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

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+# Crunchy
+
+The crunchy unroller - deterministically unroll constant loops. For number
+"crunching".
+
+The Rust optimizer will unroll constant loops that don't use the loop variable,
+like this:
+
+```rust
+for _ in 0..100 {
+  println!("Hello!");
+}
+```
+
+However, using the loop variable will cause it to never unroll the loop. This is
+unfortunate because it means that you can't constant-fold the loop variable, and
+if you end up stomping on the registers it will have to do a load for each
+iteration. This crate ensures that your code is unrolled and const-folded. It
+only works on literals, unfortunately, but there's a work-around:
+
+```rust
+debug_assert_eq!(MY_CONSTANT, 100);
+unroll! {
+  for i in 0..100 {
+    println!("Iteration {}", i);
+  }
+}
+```
+
+This means that your tests will catch if you redefine the constant.
+
+To default maximum number of loops to unroll is `64`, but that can be easily increased using the cargo features:
+
+* `limit_128`
+* `limit_256`
+* `limit_512`
+* `limit_1024`
+* `limit_2048`
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