Adds command for normalizing {{ tag }} spacing

This command uses the `sed` command line tool to replace tags such as
the following:

    {{no_spacing}}
    {{uneven_spacing }}
    {{ uneven_spacing}}
    {{    too_much_spacing }}
    {{someone_was_drunk      }}

...and so on.  The same replacements are made for {% block %} syntax.
All tags are normalized to have just one space after/before the
open/close token.