expose debug as default export

[ghost]

• Similar to tj/co
• Allow to re-export debug from another module in ES6

Without this fix, it is troublesome to re-export debug from a module. Basically, the following will not compile / debug will not be correctly exported as it should:

// my utilities
export myLog () {}
export * from "debug" // just re-export debug 
...

[ghost]

Thanks

[101100]

Any plans to release this on npm soon?