0.5.3

- Added `-bar` option to the commands so that they can be written one line
  with BARs. e.g. `PlugClean! | PlugInstall`
- Fixed `PlugUpgrade` so that a restart (or reload of .vimrc) is not required
  even when a very old version of vim-plug is upgraded
- Removed redundant code for creating of `g:plug_home` directory
