add cmake usage example

examples/cmake/.gitignore

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+/build

examples/cmake/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.10)
+
+include(FetchContent)
+FetchContent_Declare(hacl
+    DOWNLOAD_EXTRACT_TIMESTAMP TRUE
+    GIT_REPOSITORY https://github.com/cryspen/hacl-packages/
+    GIT_TAG 88560a8b5bae5db890e11f1ea71376adfa767baf
+)
+FetchContent_MakeAvailable(hacl)
+
+project(hacl-blake-example)
+set(CMAKE_OSX_ARCHITECTURES arm64)
+
+add_executable(example blake-example.cc)
+
+# Add includes from HACL
+target_include_directories(example PRIVATE
+    ${hacl_SOURCE_DIR}/include
+    ${hacl_SOURCE_DIR}/build
+    ${hacl_SOURCE_DIR}/karamel/include
+    ${hacl_SOURCE_DIR}/karamel/krmllib/dist/minimal
+    ${hacl_SOURCE_DIR}/vale/include
+)
+# Link the HACL library
+target_link_libraries(example PRIVATE hacl)

examples/cmake/Readme.md

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+# CMake Example
+
+This folder contains an example for how to use the HACL Packages C library in a
+CMake project.
+
+```sh
+mkdir build
+cd build
+cmake ..
+cmake --build .
+./example
+```

examples/cmake/blake-example.cc

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+/*
+ *    Copyright 2022 Cryspen Sarl
+ *
+ *    Licensed under the Apache License, Version 2.0 or MIT.
+ *    - http://www.apache.org/licenses/LICENSE-2.0
+ *    - http://opensource.org/licenses/MIT
+ */
+#include "Hacl_Hash_Blake2.h"
+
+using namespace std;
+
+void print_hex_ln(size_t bytes_len, uint8_t *bytes)
+{
+    for (int i = 0; i < bytes_len; ++i)
+    {
+        printf("%02x", bytes[i]);
+    }
+
+    printf("\n");
+}
+
+int main(int argc, char const *argv[])
+{
+    // Reserve memory for a 64 byte digest, i.e.,
+    // for a BLAKE2B run with full 512-bit output.
+    uint32_t output_len = 64;
+    uint8_t output[64];
+
+    // The message we want to hash.
+    const char *message = "Hello, HACL Packages!";
+    uint32_t message_len = strlen(message);
+
+    // BLAKE2B can be used as an HMAC, i.e., with a key.
+    // We don't want to use a key here and thus provide a zero-sized key.
+    uint32_t key_len = 0;
+    uint8_t *key = 0;
+
+    Hacl_Blake2b_32_blake2b(
+        output_len, output, message_len, (uint8_t *)message, key_len, key);
+
+    print_hex_ln(output_len, output);
+
+    return 0;
+}