Add Pandas.jl

[davidanthoff]

@malmaud This makes a Pandas.jl DataFrame an IterableTables.jl source. There are still some issues:

• When I call values(df[i]) on a column with strings, I don't seem to get a Vector{String}, but instead this:

  
  julia> df
  age   name
  0   27  James
  1   29   Jill
  2   27   Jake

julia> values(df[:name]) 3-element Array{Ptr{PyCall.PyObject_struct},1}: Ptr{PyCall.PyObject_struct} @0x0000000026f58e90 Ptr{PyCall.PyObject_struct} @0x0000000026f58dc8 Ptr{PyCall.PyObject_struct} @0x0000000026f58f58

Any way for me to get a normal ``Vector{String}`` there?
- Also, what would I get for a column that has missing values?

I'll look at making it a sink soonish.

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Codecov Report

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@@            Coverage Diff            @@
##             master      #42   +/-   ##
=========================================
  Coverage          ?   79.54%           
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  Files             ?       16           
  Lines             ?      621           
  Branches          ?        0           
=========================================
  Hits              ?      494           
  Misses            ?      127           
  Partials          ?        0

Impacted Files	Coverage Δ
src/IterableTables.jl	100% <ø> (ø)
src/integrations/pandas.jl	0% <0%> (ø)

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[davidanthoff]

Closed in favor of JuliaPy/Pandas.jl#20.