Don't squash words together

Markdown paragraphs with multiple linebreaks and no whitespace at
the end of each line would end up with words running together.
By joining them with a space in between, we don't accidentally
merge them.
Set is_teaser on a per-post basis

Dynamically decided based on whether or not there is more content
to show beyond the initial paragraph.
Merge pull request #11 from clee/patch-1

Small enhancements to index_helper