Allow plan plugin to read from $PLENV_ROOT (useful with Homebrew on Mac).
Merge pull request #282 from janlindblom/feature/improved_plenv_plugin

Allow plenv plugin to read from $PLENV_ROOT
Add _prepend_tree command. Traverse a dependency tree and add it to a path.
Add -P --preview flag to help debug/test command.
Merge pull request #280 from bucaran/feat-prepend_tree
add capability to bash `export`
Merge pull request #278 from jcouyang/export
Merge branch 'master' of https://www.github.com/bpinto/oh-my-fish into feat-prepend_tree