resolves issue #58 by upgrading haml version.
resolves issue #20, by providing scripts to execute Asciidoctor in linux
and windows, without installing Ruby environment.
resolves issue #57 by changing ORIGINAL_ADMONITION_ICONS_WITH_IMG to
IMAGE_ICONS and FONTAWESOME_ADMONITION_ICONS to FONT_ICONS
resolves issue #55 by printing usage when no argument is set.
resolves issue #54 by providing a method to initialize attributes
builder with all attributes at once.
resolves issue #59
resolves issue #60.