Add pyenv plugin

plugins/pyenv/pyenv.plugin.zsh

+_homebrew-installed() {
+    type brew &> /dev/null
+}
+
+_pyenv-from-homebrew-installed() {
+    brew --prefix pyenv &> /dev/null
+}
+
+FOUND_PYENV=0
+pyenvdirs=("$HOME/.pyenv" "/usr/local/pyenv" "/opt/pyenv")
+if _homebrew-installed && _pyenv-from-homebrew-installed ; then
+    pyenvdirs=($(brew --prefix pyenv) "${pyenvdirs[@]}")
+fi
+
+for pyenvdir in "${pyenvdirs[@]}" ; do
+    if [ -d $pyenvdir/bin -a $FOUND_PYENV -eq 0 ] ; then
+        FOUND_PYENV=1
+        export PYENV_ROOT=$pyenvdir
+        export PATH=${pyenvdir}/bin:$PATH
+        eval "$(pyenv init --no-rehash - zsh)"
+
+        function pyenv_prompt_info() {
+            echo "$(pyenv version-name)"
+        }
+    fi
+done
+unset pyenvdir
+
+if [ $FOUND_PYENV -eq 0 ] ; then
+    function pyenv_prompt_info() { echo "system: $(python -V 2>&1 | cut -f 2 -d ' ')" }
+fi