Potential backwards-incompatible [for rocket-chip] changes to be made in Chisel3

[hcook]

• package Chisel => package chisel
• chiselMain => Driver.elaborate (with no wrapping of top level module)
• trait FileSystemUtilities => object FileUtils
• remove Module and Bundle factory methods that apply new params as partial functions => paramsScope

[chick]

@hcook does this need to be open still?

[ducky64]

Rocket-chip will stay on the compatibility layer.

We are no longer planning to rename chisel3 -> chisel, and Chisel will remain as the compatibility package.