Add pip plugin to support upgrade/uninstall all packages.

plugins/available/pip.plugin.bash

@@ -0,0 +1,23 @@
+pip-upgrade-all() {
+    local outdated_packages="$(pip list --outdated --format=freeze | grep -v '^\-e' | cut -d = -f 1)"
+    if [ -z $outdated_packages ]
+    then
+        echo "pip: everything is up to date."
+    else
+        for package in $outdated_packages; do
+            pip install --user -U $package
+        done
+    fi
+}
+pip-uninstall-all() {
+    local installed_packages=pip list --user --format=freeze | grep -v '^\-e' | cut -d = -f 1 
+    if [ -z $installed_packages ]
+    then
+        echo "pip: nothing has been installed."
+    else
+        for package in $installed_packages; do
+            pip uninstall -y $package
+        done
+    fi
+}
+