sha: merge sha1/sha256 handling (they are similar enough for this),

sha: merge sha1/sha256 handling (they are similar enough for this),
 shrink sha215 code

function                                             old     new   delta
sha1_end                                             129     142     +13
sha1_process_block64                                 486     494      +8
sha256_begin                                          37      44      +7
sha1_begin                                            49      56      +7
sha1_hash                                            108     112      +4
...
sha512_end                                           204     184     -20
sha512_process_block128                             1405    1334     -71
sha256_process_block64                               520     446     -74
sha256_end                                           147       -    -147
sha512_hash                                          297     130    -167
sha256_hash                                          260       -    -260
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 11/9 up/down: 59/-752)         Total: -693 bytes