Added independent chart examples.

This PR fixes #1014.
Ok I am ok with this as a stopgap it is still a clear improvement. LGTM 



> On Aug 22, 2014, at 9:55, Damián Avila <notifications@github.com> wrote:
> 
> In examples/charts/boxplot.py:
> 
> > +# we throw the data into a pandas df
> > +from bokeh.sampledata.olympics2014 import data
> > +df = pd.io.json.json_normalize(data['data'])
> > +
> > +# we filter by countries with at least one medal and sort
> > +df = df[df['medals.total'] > 0]
> > +df = df.sort("medals.total", ascending=False)
> > +
> > +# then, we get the countries and we group the data by medal type
> > +countries = df.abbr.values.tolist()
> > +gold = df['medals.gold'].astype(float).values
> > +silver = df['medals.silver'].astype(float).values
> > +bronze = df['medals.bronze'].astype(float).values
> > +
> > +# later, we build a dict containing the grouped data
> > +medals = dict(bronze=bronze, silver=silver, gold=gold)
> I completely agree... what you propose is the "input machinery" we still need to develop in charts, and I am working on that on top of the refactoring PR... we need some abstraction to be able to take any reasonable input and throw it into the chart plotting machinery. Currently, that mechanism is limited, so this is the cause I have to do the astype and dict business.
> You can see that in other charts types like scatter is easier to throw a pd object because you have x and y... in this case is a little bit complex, and we have to be more intelligent...
> In any case, I think we can improve this example later, after working in the "input machinery" I mentioned above...
> 
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