Provide interfaces for other layout tools

[patrickschulz]

Currently, only an interface to cadence virtuoso is provided. It is pretty easy to write these interfaces, as they only have to call the main.lua with the correct cell, retrieve the filename from standard output (but also a standardized filename could be used) and then read the points from the file. The file can have any format, but I would suggest using the one used in virtuoso.lua as it's easy to write, read (by humans) and read (by computers). I'm mainly working with virtuoso, that's why this is the only interface I've provided. Therefore I need people with access to other tools.