…issues

rather than insist that developers use pyenv and have a pyenv-virtualenv with the name suggested by .python-version, we'll only record this name (with current python version included) here.

a subsequent bootstrapper can set this up as before (via symlink) or suggest how to customize (locally)

based on [dssg/install-cli]

resolves #444
resolves #456

changes:

* the repository no longer insists on a pyenv virtualenv via the file
.python-version, and otherwise avoids edge cases wherein this file caused
issues
* a bootstrap "wizard" script makes recommendations -- heavily reliant
on pyenv -- but which the developer may opt in or out of, (and instead
use more as an interactive checklist)

the script **prompts** to do the following:

* install pyenv
* install the python version now reflected by .python-version.current
  (the _check_ does not assume pyenv; but, it does not support
  _installation_ of the expected python version without pyenv)
* install a pyenv virtualenv named like what's in .python-version.current
* write a symlink .python-version to enable auto-activation of the
  virtualenv (if the pyenv virtualenv was created)
* pip install all development dependencies
* pip install "editable" / in "develop mode" the triage library itself

and slightly expanded subsequent pyenv-dependent checks

…environment via `develop` script