Support for self-hosted js-envs Lumo and Planck

[mfikes]

Fixes #116

This PR adds the ability to to lein doo lumo and lein doo planck.

Detailed notes:

Self-hosted ClojureScript doesn't require the ClojureScript compile build step (as lumo and planck operate directly on source, compiling in memory internally). So, in theory, while the build step is harmless, it could be omitted. But, it wasn't clear to me how this could be easily accomplished when the auto mode is in effect (because the ClojureScript compiler's watch capability is used). So, this PR does nothing with respect to the build step and preserves the existing logic.

Also, since lumo and planck don't need the results of the build, the (:output-to compiler-opts) final script runner command line argument is conditionally omitted for the self-hosted testing case. (If you look at the way lumo and planck are executed, they are directed to run the test by issuing a require on the (:main compiler-opts).

I tried putting some of the self-hosted stuff into a separate namespace, with defmethods for :lumo and :planck, which would be an appealing approach, but it is difficult to cleanly do this without wanting a circular dependency between doo.core and that new separate namespace. So this PR just keeps it simple and puts the self-hosted support directly in doo.core.

This PR works with the current lumo release.

For planck recently-released version 2.14.0 is required, otherwise two issue arise which could be worked-around in doo but they are really planck defects:

• Planck defect Need to load REPL code when initializing engine planck-repl/planck#737 causes doo.runner to be reloaded after having set the doo.runner/*exit-fn*. A doo workaround would be to employ defonce, but this has been fixed in Planck 2.14.0.
• Planck defect If exit called, exit immediately planck-repl/planck#735 causes doo complain that the *exit-fn* hasn't been properly set, owing to an artifact where Planck internally uses exceptions when planck/exit is called; this also has been fixed in Planck 2.14.0 thus making it compatible with the way doo catches :default

[bensu]

Looks good, thanks! Can you please add the plank version requirements to the README?

[mfikes]

Added Planck version requirement to README.

[bensu]

Thanks @mfikes! I'll let @miikka cut the next release when he feels it is ready. He has a better grasp on the latest, unreleased work.