add execute request pipe. Fixes #572, #411

[EstebanFuentealba]

There was a breaking change in the Cloud Functions setup that triggered this issue. It has to do with the way the middleware works that gets applied to all Express apps (including the default app) used to serve HTTPS functions. Basically, Cloud Functions will parse the body of the request and decide what to do with it, leaving the raw contents of the body in a Buffer in req.rawBody.

I added a parameter in the configuration to be able to manipulate the call to busboy. Fixes #572, #411

[marvin-j97]

^ This would be great.

[paaKways]

why hasn't this been merged already though?

[reinaldoacdc]

This would be great.