pycall api updates

[stevengj]

PyCall 1.90.0 is now released, which change o[:foo] and o["foo"] to o.foo and o."foo", respectively, for python objects o; see also JuliaPy/PyCall.jl#629.

The old getindex methods still work but are deprecated, so you'll want to put out a new release that uses the new methods and REQUIREs PyCall 1.90.0 to avoid having zillions of deprecation messages.