Commit 27. Major update - {{else}} with any tag, {{include}} etc.

1: All tags now support one or more {{else}} tags
 - not only {{if ...}}...{{else ...}}...{{else}}...{{/if}}
 - but also {{for ...}}...{{else ...}}...{{else}}...{{/for}}
 - or {{myTag ...}}...{{else ...}}...{{else}}...{{/myTag}}.

 The {{else}} tag(s) will in effect split the content of the
 {{myTag}}...{{/myTag}} block into multiple blocks.

 Each tag implementation can define specific behavior for the {{else}}
 blocks.

 Example: Add an {{else}} to {{for}}...{{/for}} to provide an
 'if array is empty' section.

 - See http://borismoore.github.com/jsviews/test/test-pages/for-else.html
 for an advanced interactive example with JsViews.
 - See the updated http://borismoore.github.com/jsviews/demos/tag-controls/tabs-control.html
 for an interactive example of {{myTag}}...{{else}}...{{/myTag}}

2: There is now an {{include tmpl=.../}} tag, for simple template
 composition, without navigation through data, or iteration over arrays.
 See issue #155

3: There is now a new ‘wrapped template’ feature for providing both
 a template  and block content, so that the template can then ‘wrap’
 the content.
 See http://borismoore.github.com/jsrender/demos/step-by-step/06_template-composition.html

BREAKING CHANGES:
The tag.renderContent() method has been replaced by tag.tagCtx.render()
 on each tagCtx
 See http://borismoore.github.com/jsrender/demos/step-by-step/08_custom-tags.html.

Advanced custom tag APIs have changed for better support of {{else}} blocks,
 and better navigation through the tag hierarchy.