crypto: make public all Digest.checksum() methods

vlib/crypto/sha1/sha1.v

@@ -102,8 +102,8 @@ pub fn (d &Digest) sum(b_in []byte) []byte {
 	return b_out
 }
 
-// checksum returns the byte checksum of the `Digest`.
-fn (mut d Digest) checksum() []byte {
+// checksum returns the current byte checksum of the `Digest`.
+pub fn (mut d Digest) checksum() []byte {
 	mut len := d.len
 	// Padding.  Add a 1 bit and 0 bits until 56 bytes mod 64.
 	mut tmp := []byte{len: (64)}

vlib/crypto/sha256/sha256.v

@@ -142,7 +142,8 @@ pub fn (d &Digest) sum(b_in []byte) []byte {
 	return b_out
 }
 
-fn (mut d Digest) checksum() []byte {
+// checksum returns the current byte checksum of the Digest.
+pub fn (mut d Digest) checksum() []byte {
 	mut len := d.len
 	// Padding. Add a 1 bit and 0 bits until 56 bytes mod 64.
 	mut tmp := []byte{len: (64)}

vlib/crypto/sha512/sha512.v

@@ -214,7 +214,8 @@ pub fn (d &Digest) sum(b_in []byte) []byte {
 	return b_out
 }
 
-fn (mut d Digest) checksum() []byte {
+// checksum returns the current byte checksum of the Digest.
+pub fn (mut d Digest) checksum() []byte {
 	// Padding. Add a 1 bit and 0 bits until 112 bytes mod 128.
 	mut len := d.len
 	mut tmp := []byte{len: (128)}