Remove validation conditionals.

The validate module will be used by the server before executing any
commands rendering any validation here useless.
Remove hasCommand().

Validate module will check if the command is valid or not.
Remove all type validation.

Should be handled by the validate module prior to invoking database
methods. Add stub sorted set class.
Remove private namespace.

No longer an issue now that the validate module performs all validation
ahead of time,
Update database comments, mget/mset test specs.
0.1.17
Settle on type declaration.

Extending Array and testing on Array.isArray() is a bad idea, adding
non-enumerable properties with Object.defineProperty() will likely
result in property conflicts so decide to use composition with a type
field.

This enables fast type validation and makes the TYPE command quick to
implement.
0.1.18
Draft hash map functions.
0.1.19