Split into global and local modes

This release separates dtrt-indent into two minor modes, a buffer-local mode (dtrt-indent-mode) and a global mode (dtrt-indent-global-mode). If you are currently using (dtrt-indent-mode 1) in your emacs configuration, replace it with (dtrt-indent-global-mode 1) to maintain the current behavior of activating dtrt-indent-mode in all buffers. Alternatively, dtrt-indent-mode can be activated with a hook, eg (add-hook 'find-file-hook 'dtrt-indent-mode), for more granular control over which buffers will be affected.