Suppress activate/deactivate messages by default

change minor typo in bin/pyenv-sh-activate

Evaluate ${PATH} when outputted code is eval'd.

`pyenv virtualenvs` lists two entries for each virtualenv

It was previously evaluated when 'pyenv virtualenv-init' is run.

Clarification of auto-activation/deactivation feature

Add envs/*/my-virtual-env dir for uninstall

Both directories need to be deleted or a subsequent install with the same name will fail

pyenv install 3.4.3 my-virtual-env:
rm -rf ~/.pyenv/versions/my-virtual-env ~/.pyenv/versions/3.4.3/my-virtual-env

`pyenv virtualenv-init` is just an option. Always showing message about
it would be too much to do.

Use `conda create` to create virtual environment if `conda` is available