chore(deps): removes purell from dependancies

[erraggy]

This adds an internal implementation of what was consumed from the
purell module by copying only the bits that were ultimately
consumed.

All tests still pass.

Issue: #10

[erraggy]

Thank you for the prompt review/approval/merge! I was curious if a new release tag would be created? Not in a rush, I just wanted to remove the purell dependency from some other projects that depend on this as well.

Thanks again.

[casualjim]

Thanks for the poke, I pushed a new tag v0.20.0

[erraggy]

Oy, and I'm just now realizing my projects pull this in via go-openapi/spec and not directly.
https://github.com/go-openapi/spec/blob/master/go.mod#L5

Not sure how many other go-openapi modules also depend on it. Maybe y'all have a job that bumps dependencies across your modules?

I poked around and only found one other: https://github.com/go-openapi/analysis/blob/master/go.mod#L5

[erraggy]

Thanks again @casualjim !!!

I see you've already addressed these and new release tags have been created.