get_entries is now sending multiple queries.
signatureAlgorithm should be the same as signature
Slightly refactored test and log_client.
Async log client now also retries on parse errors.

Changed method that creates get-entries request so it always adds
parse entries callback. Thanks to that response errorback catches
errors both from request and parsing.
Changed creating request to use 0 retries delay.

Also slightly changed formula and flags, so effects are similar to
previous state.
Added methods for getting signature algorithms.
Character set checking for few of ASN.1 strings.