Add --bare option to `pyenv version`

[jjwatt]

It just points at pyenv version-name. This adds consistency with the behavior of pyenv versions --bare

Make sure you have checked all steps below.

Prerequisite

• [x] Please consider implementing the feature as a hook script or plugin as a first step.
  • pyenv has some powerful support for plugins and hook scripts. Please refer to Authoring plugins for details and try to implement it as a plugin if possible.
• [x] Please consider contributing the patch upstream to rbenv, since we have borrowed most of the code from that project.
  • We occasionally import the changes from rbenv. In general, you can expect changes made in rbenv will be imported to pyenv too, eventually.
  • Generally speaking, we prefer not to make changes in the core in order to keep compatibility with rbenv.

I don't use rbenv, but from a quick look, I could make a similar change there. However, the files in question are already different (though the behavior is similar).

• [] My PR addresses the following pyenv issue (if any)
  • Closes https://github.com/pyenv/pyenv/issues/2779

Description

• [x] Here are some details about my PR Adds a --bare flag to pyenv version

Tests

• [ ] My PR adds the following unit tests (if any)

[native-api]

Please add a test for the new option.

[jjwatt]

Sure thing! bats for testing. Excellent. I think I see just where to add it.

[anton-petrov]

@jjwatt Hi, so what about tests? I think, PR is ready for merge, except of tests.