#418 Generate global variables in new PLC code generator

Variables are here!

• Adding several generators (for a wide notion of "generator").
• Cif processor is likely doing a bit too much with enumerations currently.
• Not sure the type generator is the final spot for enumerations, but that will sort itself out once we get expressions.
• Switched int type selection to an option for setting the desired type rather than the maximum type. Added a float version as well.
• Needed to drag in the S7 writer, as it didn't allow writing other variable tables.
• Added a simplified "all1.cif" test to the testfiles, the original file uses many features currently not processed.

Next step is expressions, for constants and variable initialization (in variable tables).

Reading one commit at a time is likely simplest.

Adresses #418 (closed)