First version of sklearn intro IPython Notebook
Removed lesson number
Added an outline

Also removed a cell
Print number of samples in the dataset
Use StandardScaler instead of scale

For simplicity just scale all of the dataset for
grid search.
see: https://github.com/swcarpentry/bc/pull/443#issuecomment-40677511
Optimize max_features instead of n_estimators

Useless to estimate n_estimators, the more the better!
Use a Pipeline to add feature scaling
Removed feature scaling, expanded acronym RMS

Feature scaling is not necessary for Decision Tree and Random Forests:
https://github.com/swcarpentry/bc/pull/443#issuecomment-41324381
Remove import of Pipeline
added conclusion
Replaced Iris example

Iris example was not clear, replaced with another example.
Added also svg and Google Docs url.

Minor changes:
* explain del rings
* removed download of dataset, just link
Fix headings for book

Some Markdown files start with

    ---
    layout: lesson
    root: .
    title: TITLE
    ---
    ### SUBTITLE

When creating `book.md` it will have

    ## TITLE
    ### SUBTITLE

that is translate into HTML by Jekyll as

    <h2>TITLE</h2>
    <p>### SUBTITLE</p>

Change `make-book.py` to generate `book.md` having

    ## TITLE

    ### SUBTITLE

will fix this issue without side effect.

Thanks to @jduckles for reporting this issue.
Merge pull request #545 from r-gaia-cs/fix-book-h2

Fix headings for book
Fixes #546 by using level-3 headings in all Markdown source files for subsections.
We continue to use level-4 headings for objectives, key points, callout boxes, and challenges.
Fix more level 3 headings
Merge pull request #548 from gvwilson/using-level-3-headings-for-subsections-in-markdown

Using level-3 headings in Markdown files for subsections.
Merge pull request #443 from zonca/intro-sklearn-abalone

introduction to scikit-learn lesson