Drop requirement for Bluebird

[nickshanks]

Please can you consider for the next major version dropping the requirement for Bluebird, and falling back to native javascript promises if no PromiseImpl is provided. Clients that want to retain Bluebird can then include it themselves and provide it to you.

[nickshanks]

In the mean time, could you move the require('bluebird') call into if(!PromiseImpl) in the same way that require('mysql') is only called if it needs to be.

[CreativeWarlock]

Looks like noone in the JS world is willing to do anything anymore. Last commits date years back for many projects. For newcomers it looks like support / modules for JS are slowly drying out.