Refactor imagine

[shaqque]

This pull request refactors imagine as a package to make it easier for other tools to import the imagine tool. Also fixes some linter issues.

[shaqque]

It looks like most of the diffs are just renaming the package, which is fine. I can't convince github to show me the actual diffs to main.go. It may be better to combine the two commits, I think github (and git) will have a better handle on displaying this.

I didn't know how to combine the commits into one, but I'll work on that!

But the reason for "request changes" is that it looks like imagine/main is a 13MB binary file added by the first commit, and that should probably be removed from the commit.

good catch. I completely forgot about this after testing.

Usage question: Say I wanted to have a command-line imagine tool. Do we still have one, or do we only have the package? Can we get a trivial cmd/imagine or whatever that will give us that? Or do we have one and I'm just slow today?

The tree structure in tools/imagine under the pull request is

├── README.md
├── main.go
├── pkg
│   ├── [[ enums stuff here ]]
│   ├── generators.go
│   ├── generators_test.go
│   ├── main.go
│   └── spec.go
├── sample.md
├── sample.toml
└── samples
    ├── [[ sample stuff here ]]

where the top-level main.go imports the imagine package in pkg, so we still get imagine on the command line.

[seebs]

Okay, that makes sense.

git rebase -i HEAD~2, change the second "pick" to "squash", is an approximation of how to combine the commits. (I probably forgot a step or something.)