Static classes

[lofcz]

• all members must be static
• can't be instantiated
• can't be used as a base class
• can't contain a constructor

Also adds missing LoopChk and BaseChk to InstructionFieldUsage, tests expected to crash no longer have to provide a blank file with expected stdout.

Test 23 is currently failing (point 2 above)

Fixes a bug introduced in #52, see test 25 for details.

[CallumDev]

Most of the way there, a couple of small changes - and unfortunately I think GetDescription<T> breaks a couple of use cases that I am aware wattlescript is currently being used for.