Merge branch 'hotfix/1.0.4'

Closes #28.
Guard autocommand in group

This prevents a few undesirable cases, such as:
* the autocommand being defined, or loaded, multiple times and;
* the autocommand, being defined in the default group, being called from places
  other than this script.

References #29.

Conflicts:
	plugin/niji.vim
Bump version number
Merge branch 'hotfix/1.0.5' into develop

Conflicts:
	plugin/niji.vim