Properly design coupled transmission lines

[spiccinini]

We are using coupled microstrips for the MegaBoard differential pairs (PCIe, USB, etc) and we are not taking in consideration the distance between the line and the groud plane at the sides.

Related to #54

[xcancerberox]

We have done some research and there is a constrain for the distance between differential pairs of 20mils. We will assume that the distance between the differential pair and other signals must be at least that amount. The ground planes in the same side of the differential pairs must be moved.

[xcancerberox]

The stitching vias are not need. Remove.
Add vias side to side with the vias of side change.