plotter: new classes for axes-centric plotting

    - plotter.fig: defines simple extension of mpl Figure
    - plott.axes: defines simple extension of mpl Axes
plotter.ticks: fix bug in epoch checking
plotter.auto_refresh: allow auto_refresh of axes
plotter.timeseries: added TimeSeriesAxes

    - new Axes sub-class for displaying TimeSeries on Plots
plotter: setup new axes-based plotting imports

    - provides pyplot-style figure() generator function
plotter.Plot: bug fix in fig.py
plotter: new TimeSegmentAxes class and mods

    - new plot_timeseries method for TimeSeriesAxes
    - new plot_xxx methods in TimeSeriesAxes for adding segments
    - new TimeSegmentAxes class
TimeSeries.psd: minor type casting fix
SpectrumAxes: new plot axes

   - designed for display of amplitude/power versus frequency
Series: bug fix in metadata ownership when slicing
Series: improved index property
Array2D: improved index_x, index_y properties
Array2D: now return span_x, span_y as Segment
TimeSeriesAxes: added plot_spectrogram

    - pcolormesh spectrogram plotter, handles logarithmic scales nicely
fix whitespace errors
auto_refresh: now returns function output
auto_refresh: fix corner case of attribute get
Plot: new add_colorbar method

    - generates a new colorbar axes on the current plot, mapping against
      a collection (mappable) and its axes
TimeSeriesAxes: added auto_refreshing to methods
Series: bug fix in index property