Hotfix/ascii opcode endianness

[200sc]

This PR fixes two compatibility issues with rainway's compiler; it:

• Corrects the endianness of ASCII string encoded opcodes
• Enforces that opcodes are all unique

In addition we have more testdata and internally represent opcodes as uint32s instead of int32s.

Closes #29

[merlindru]

Thank you for the incredibly fast turnaround!

[200sc]

@merlindru I'll take that as 'this works', and merge it in with a version bump later today!