added basic plot recipe

[mkborregaard]

This adds basic plotting functionality to TimeArray objects, with a very light dependency (RecipesBase a single macro). It allows plotting as simply as plot(ohlc).
Discussed here JuliaPlots/StatPlots.jl#37 (comment) and here #302 .

The current recipe will plot all values in the array, which may not make sense if they are not on the same scale, but you can always plot(ohlcv["Volume"]).

[ararslan]

Please use 4 space indents for consistency with the rest of the repository

[coveralls]

Coverage decreased (-0.8%) to 96.275% when pulling d732cc6 on mkborregaard:recipe-for-time-arrays into 7928b8f on JuliaStats:master.

[milktrader]

Coverage will be fine maybe increase with some tests

[mkborregaard]

Do you need me to write a line for the docs (in which case where?) or will you leave this implicit?

[milktrader]

If you can think of a reasonable test it would be great. But if it doesn't do anything but move the coverage then no.

[dourouc05]

@mkborregaard: As a user, I'd appreciate a bit of doc about this (at least, say that it exists, maybe briefly how to make a basic plot — i.e. using Plots and plot(time series) — and a link to Plots).

[mkborregaard]

Sure - where in the docs should it go?

[dourouc05]

In getting started? Customize how TimeArray is displayed could also be interesting, but I don't feel at ease with the idea of putting plots there.

[milktrader]

I was planning a new section called simply Plotting

[milktrader]

If you want to start a file called plotting.rst I can make the links. I would copy an existing .rst file for the format template.

[mkborregaard]

No probs. It will be a little while cause I'm going on holiday now.

[mkborregaard]

Here you are #305
I have started it up, can you take it from here?