Add binary-safe alternatives for eval

[mspielberg]

Currently the only externally accessible commands for EVAL and friends take Seq[String] for keys and arguments. String can only contain valid UTF-8 sequences, which makes it impossible to send arbitrary binary data to a Lua script, for example to do a compare-and-set of compressed data.

This exposes a new evalBinary method and related equivalents that expose the ability for an application to provide its own ByteStringSerializer instances for arguments to scripts. Note these can't easily be written as simple overloads because the erased type of the arguments (Seq[_]) would be identical to the existing Seq[String] methods.

[coveralls]

Coverage increased (+0.02%) to 90.735% when pulling de38924 on mspielberg:master into 55573df on etaty:master.

[btd]

Ping @etaty .This PR very useful, i hit exactly the same limitation.