Modify Record struct to support all possible format.

[aitjcize]

Allow the Record struct to record all the attribute of different formats including Gerber/ODB++/IPC2581. This way, record can act as a intermediate representation of general PCB layout format. We can than implement different export engines to export the record into Gerber/ODB++/IPC2581. By doing this, we can convert between different file formats.