v0.0.7
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* Add option `--use-prebuilt` for command `oo get`, default to `false`.
* Downloads a prebuilt package from golang.org/dl for the first installation via `oo get`.
* Fix issues in `oo ls` and `oo` when no version installed.

v0.0.6
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* Display a prefix `=>` for activated version in command `oo ls`.
