Module ports beyond io

[grebe]

It is my understanding that firrtl doesn't care what input and output ports of a module are named. The current chisel3 frontend has a private variable called ports that is only clk, reset, and io.

I propose that we make this variable protected instead of private.

This will allow people to have input/output ports outside of the IO bundle, making chisel3 match firrtl more closely.

[aswaterman]

Depending on the use case, #156 and/or #157 may satisfy the demand.

[chick]

@grebe should this be open at this point

[ducky64]

Discussion should continue in #469 and #427