Signature help

[aazuspan]

Closes #5 by implementing signature help. Other changes:

• Reformatted opcode documentation to be more readable as hovers and as signature help. Mostly that meant removing the big header and editing the description to always start with the function signature.
• Reorganized the documentation modules by moving all the markdown generators into the markdown module, leaving the instructions and assemblers modules as purely documentation.
• Reorganized server tests so that each feature is tested in a separate file which contains both the tests and the test cases.