Supports options.db to select redis db

[hyjin]

Hi, this change enables selecting db with options.db.

For example,

var emitter = new devents.EventEmitter({
    host: 'machine1.company.com',
    port: 6379,
    db: 1
});

[andyburke]

I'll accept this PR after a couple of cosmetic changes to conform to the rest of the code style:

1. Spaces should be used with parens
2. Braces for if statements should be on their own line

Example:

if ( condition )
{
    someFunction( someArgument );
}

[hyjin]

@andyburke Here is update for code style. Thank you!