added decrypt file feature.
fix reference to aes256_decrypt
fix minor bugs
add execute to scripts
unified s3_crypto helper script.  updated README.rdoc
Fixing bugs.  Added buffered md5 and sha256 checksum generation to prevent memory issues. Updated documentation.
fixing bad get_md5_from_s3 call.
fix typo
Merge pull request #25 from joekiller/decrypt

Decrypt S3 files