Refactor checksum code, and add Objectname hashing per uploaded objects

Add placeholder sha256, sha512 implementations from Intel with AVX, AVX2
and SSE4.1 extensions - with some boilerplate Go code.

pkgs/crypto/sha256/sha256.go

@@ -0,0 +1,39 @@
+// +build amd64
+
+package sha256
+
+// #include <stdint.h>
+// void sha256_transform_avx (uint8_t *input_data, uint32_t digest[8], uint64_t num_blks);
+// void sha256_transform_ssse3 (uint8_t *input_data, uint32_t digest[8], uint64_t num_blks);
+// void sha256_transform_rorx (uint8_t *input_data, uint32_t digest[8], uint64_t num_blks);
+// #define SHA256_DIGEST_SIZE      32
+// #define SHA256_BLOCK_SIZE       64
+// #define SHA256_H0       0x6a09e667UL
+// #define SHA256_H1       0xbb67ae85UL
+// #define SHA256_H2       0x3c6ef372UL
+// #define SHA256_H3       0xa54ff53aUL
+// #define SHA256_H4       0x510e527fUL
+// #define SHA256_H5       0x9b05688cUL
+// #define SHA256_H6       0x1f83d9abUL
+// #define SHA256_H7       0x5be0cd19UL
+import "C"
+
+/*
+func Sha256(buffer []byte) ([]uint32, error) {
+
+	if cpu.HasSSE41() {
+		C.sha256_transform_ssse3()
+		return 0, nil
+	}
+
+	if cpu.HasAVX() {
+		C.sha256_transform_avx()
+		return 0, nil
+	}
+
+	if cpu.HasAVX2() {
+		C.sha256_transform_rorx()
+		return 0, nil
+	}
+}
+*/