Preprocessing

The preprocessing notebook for the American Gut data. A version of the notebook text can be found on [google docs](https://docs.google.com/document/d/1AR2GrHsVT8LjVTiRHPnn43GF_Eoz8wT5ZH3Q-Of9-BI/edit?usp=sharing). 
See this function in qiita:
https://github.com/biocore/qiita/blob/master/qiita_db/metadata_template.py#L1718-1750 should be easily adaptable for this use-case.

On (Dec-04-14|15:13), Daniel McDonald wrote:
> > +     "cell_type": "markdown",
> > +     "metadata": {},
> > +     "source": [
> > +      "<a href=\"#top\">Return to the top</a>\n",
> > +      "\n",
> > +      "<a id=\"clean_map\"></a>\n",
> > +      "#### Cleans up mapping columns\n",
> > +      "There are a set of mapping columns which are currently altered in the EBI submission. These three columns are <code>SEX</code>, <code>AGE_UNIT</code>, and <code>DOMINANT_HAND</code>. So, we will fix the values in these columns for the mapping file we plan to use in our analyses."
> > +     ]
> > +    },
> > +    {
> > +     "cell_type": "code",
> > +     "collapsed": false,
> > +     "input": [
> > +      "# Loads the mapping file and the OTU table\n",
> > +      "raw_map = pad_index(pd.read_csv(raw_map_fp,\n",
> 
> I _think_ you can just specify `dtype={'#SampleID': str}` on load instead of doing this padding as there are pathological cases where this will not work (e.g., "0001234.123000")
> 
> ---
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> https://github.com/biocore/American-Gut/pull/120/files#r21344481