Compatibility issues

[okwestern]

I propose the following changes:
sha1.cpp should be changed:
void Sha1Class::write(uint8_t data) {
to:
size_t Sha1Class::write(uint8_t data) {

uint8_t sha1InitState[] PROGMEM = {
to:
const uint8_t sha1InitState[] PROGMEM = {

sha256.cpp should be changed:
uint32_t sha256K[] PROGMEM = {
to:
const uint32_t sha256K[] PROGMEM = {

uint8_t sha256InitState[] PROGMEM = {
to:
const uint8_t sha256InitState[] PROGMEM = {

Both sha1.h and sha256.h should be changed from:
virtual void write(uint8_t);
to:
virtual size_t write(uint8_t);