Rename `RedisCommandContext` to `RedisCommand`, improve `RedisCommandHandler`...

Rename RedisCommandContext to RedisCommand, improve RedisCommandHandler usage semantics, and cleanup documentation.

Motivation:

During proposal review, it was noted that RedisCommandContext was a bit misleading, and the hidden reference semantics worrisome.

In addition, several of parts of the documentation around RedisCommandHandler were weak or also misleading.

Modifications:

• Rename RedisCommandContext to just RedisCommand
• Update documentation to be more explicit about the module who owns the types being referenced
• Update documentation to call out explicit usage semantics and behavior
• Change RedisCommandHandler to close the socket connection on error thrown
• Rename the "base" Redis Channel Handlers to be more explicitly named

Result:

Users should have clearer documentation on what happens when using RedisCommandHandler and RedisCommand without hidden semantics.

This contributes to issue #47 (closed).