Split project over multiple files

src/sha256.h

@@ -0,0 +1,9 @@
+#ifndef SHA256_INCLUDED
+#define SHA256_INCLUDED
+
+#include <stddef.h>
+#include <stdint.h>
+
+void sha256(const void *data, size_t len, uint8_t *hash);
+
+#endif // SHA256_INCLUDED