Eval function help

[jimfinnis]

Eval functions need some kind of help system:

• a help(funcname) function
• better errors when bad arguments are passed in or a function fails
• automatic docgeneration
• listing all available functions

This requires the registerFunc code to be able to handle documentation, and chkargs to be tweaked too (with arg names!) We should also make sure we use chkargs throughout, or make its use automatic. Don't add more funcs until I've thought about this.

[jimfinnis]

Coming along nicely, but does massively complicate adding a function. Here's some code now:

        self.registerFunc("grey", "convert an image to greyscale",
                          [Parameter("image", "an image to process", conntypes.IMG)],
                          [Parameter("useCV",
                                     "if non-zero, use openCV greyscale conversion (RGB input only): 0.299*R + 0.587*G + 0.114*B",
                                     conntypes.NUMBER, deflt=0)],
                          funcGrey)

So that's

• name,
• description,
• list of mandatory parameters (with name, description, type),
• list of optional parameters (ditto but also a numeric default value) (numeric for ease!)
• function that takes two lists of Datums - one mandatory, one optional.

[jimfinnis]

Now I need to provide the help function and useful error reporting using that data.

[jimfinnis]

Done, via context menus in the expression editor. Works fairly well.