Add configuration for vim

- Add ~/.config/vim/vimrc
  + Configure basic stuff
  + Activate spell checks
  + Activate syntax highlighting and ruler
  + Show whitespace characters
  + Add various snippets for mouse handling,
    toggling line numbers, and search
  + Set `vim`-related directories inside
   ~/.config/vim and ~/.local/state/vim
- Integrate extra settings for Python files
  in ~/.config/vim/after/ftplugin/python.vim
  and ~/.config/vim/after/syntax/python.vim
- Add `vim` artifacts in ~/.config/git/ignore

.config/shell/env

@@ -37,7 +37,13 @@ fi
 [ -t 0 ] && export GPG_TTY=$(tty)
 
 
-export EDITOR=nano
+if _command_exists vim; then
+    export EDITOR=vim
+elif _command_exists vi; then
+    export EDITOR=vi
+else
+    export EDITOR=nano
+fi
 
 
 export PAGER=less
@@ -68,3 +74,4 @@ export PYENV_ROOT="$XDG_DATA_HOME/pyenv"
 export PYTHONPYCACHEPREFIX="$XDG_CACHE_HOME/python"
 export PYTHONSTARTUP="$XDG_CONFIG_HOME/python/startup.py"
 export PYTHON_HISTORY="$XDG_STATE_HOME/python/history"
+export VIMINIT='let $MYVIMRC="'"$XDG_CONFIG_HOME"'/vim/vimrc" | source $MYVIMRC'