Add a way to output images of data types

[jrmoserbaltimore]

Like really just let me make a call to spit out a PNG showing the fields in here laid out like in the docs.

class Instruction(data.Struct):
    instruction: data.FlexibleLayout({
        # The last 5 are always the opcode
        "opcode": data.Field(Signal(5),27),
        "bit_ops": data.Field(data.StructLayout({
                "bitmask": Signal(24)
            }),0),
        "accumulator_ops": data.Field(data.StructLayout({
                "coefficient": Signal(16),
                "constant": Signal(11)
            }),0),
        # TODO:  SKP
        "register_ops": data.Field(data.FlexibleLayout({
                "coefficient": data.Field(Signal(16),0),
                "register": data.Field(unsigned(6),21)
            }),0),
        # TODO:  MULX?
        "dram_ops": data.Field(data.StructLayout({
                "coefficient": Signal(11),
                "address": unsigned(16)
            }),0)
        # TODO:  RMPA?  It basically ignores the address field
        # TODO: LFO, CHO
        })

[whitequark]

The lib.data module provides an introspection API that lets you do this. We don't currently have a plan to add this feature.