modified text to address issue #70

after thinking about this more, will only cover observed species here as it is intuitively the most simple way to think about alpha diversity.
added text to address #70

the unit test is failing now due to different text, and don't have time to fix it if i'm going to get through a few more issues. should we change that unit test to an ``assertTrue(result.startswith('...')). These tests that rely on text get hard to work with.
added text for top-level index page

this addresses issue #78. see the ``top_level_index_text`` varaiable. I wasn't sure where it made sense to hook it up.
Merge branch 'master' into issue-70

Conflicts:
	my_microbes/format.py
several fixes to text

 - some clarity issues (thanks @jrrideout!)
 - made email address a mailto link
 - added link to NAU144 data
Merge pull request #93 from gregcaporaso/issue-70

Issue 70