Add primitive template injection.
No need to massage argv.template since it should be properly setup already.
Rename loadSectionTemplate to be sectionTemplate.
Context is provided by "this" instead of by parameter in handleBars 1.3.x.
Allow sectionTemplate to be named [ref].html in addition to [ref].hbs.
Prevent empty markup when there is no sectionTemplate.
Add caching to sectionTemplate helper.

Reading (or attempting to read) the template from disk multiple times is super
inefficient, so we are going to cache the compiled template.
Look for section templates in the source directory.
Search for template files in sub-folders of source folder.
Add --markup option to specify location of markup handlebars files; defaults to source directory.
Update help text and code comments.
Remove sectionTemplate helper.
Allow injection of external templates into Markup section. #78
Add test for external and nested handlebars markup.
Merge pull request #78 from kss-node/pull-56-rebased

Allow injection of external templates into Markup section