Set shiftwidth to 0 (defaults to tabstop value)

[gwymor]

The current behavior is to set both shiftwidth and tabstop/softtabstop. shiftwidth gets set to the same value as tabstop. If I open a file that editorconfig indents with 8-space hard tabs, then ":set tabstop=4", my shiftwidth will still be 8, meaning that when I indent I will get two tabs. Set shiftwidth to 0, which defaults to the value of tabstop, and disable softtabstop so it doesn't conflict. This should have the same end result with less complication.

This removes the g:EditorConfig_softtabstop_space and g:EditorConfig_softtabstop_tab options. Users who want to delete multiple spaces as a single character can enable smarttab.