core:crypto/hash: Add a generic higher level hash interface

There is a lot of code duplicated in convenience methods in each hash
implementation, and having a generic hash type makes implementing
higher-level constructs such as HMAC significantly easier down the road.

core/crypto/hash/doc.odin

@@ -0,0 +1,62 @@
+/*
+package hash provides a generic interface to the supported hash algorithms.
+
+A high-level convenience procedure group `hash` is provided to easily
+accomplish common tasks.
+- `hash_string` - Hash a given string and return the digest.
+- `hash_bytes` - Hash a given byte slice and return the digest.
+- `hash_string_to_buffer` - Hash a given string and put the digest in
+  the third parameter.  It requires that the destination buffer
+  is at least as big as the digest size.
+- `hash_bytes_to_buffer` - Hash a given string and put the computed
+  digest in the third parameter.  It requires that the destination
+  buffer is at least as big as the digest size.
+- `hash_stream` - Incrementally fully consume a `io.Stream`, and return
+  the computed digest.
+- `hash_file` - Takes a file handle and returns the computed digest.
+  A third optional boolean parameter controls if the file is streamed
+  (default), or or read at once.
+
+```odin
+package hash_example
+
+import "core:crypto/hash"
+
+main :: proc() {
+	input := "Feed the fire."
+
+	// Compute the digest, using the high level API.
+	returned_digest := hash.hash(hash.Algorithm.SHA512_256, input)
+	defer delete(returned_digest)
+
+	// Variant that takes a destination buffer, instead of returning
+	// the digest.
+	digest := make([]byte, hash.DIGEST_SIZES[hash.Algorithm.BLAKE2B]) // @note: Destination buffer has to be at least as big as the digest size of the hash.
+	defer delete(digest)
+	hash.hash(hash.Algorithm.BLAKE2B, input, digest)
+}
+```
+
+A generic low level API is provided supporting the init/update/final interface
+that is typical with cryptographic hash function implementations.
+
+```odin
+package hash_example
+
+import "core:crypto/hash"
+
+main :: proc() {
+    input := "Let the cinders burn."
+
+    // Compute the digest, using the low level API.
+    ctx: hash.Context
+    digest := make([]byte, hash.DIGEST_SIZES[hash.Algorithm.SHA3_512])
+    defer delete(digest)
+
+    hash.init(&ctx, hash.Algorithm.SHA3_512)
+    hash.update(&ctx, transmute([]byte)input)
+    hash.final(&ctx, digest)
+}
+```
+*/
+package crypto_hash