psd.lal_psd: added XLAL plan and window creation

    - all auto-generated plans and windows are cached
TimeSeries.span: removed type cast
TimeSeries.{p,a}sd: added FFT plan kwarg
detector.channels: renamed import of astropy.units
Channel.texname: renamed parameter from tex_name
Channel.type: reworked to contain NDS string
io.nds: removed unused imports
ChannelList.sieve: improved sample_rate sieving
StateVector: optimisation

    - use Kipp's original from_bitstream, much faster
    - use numpy array methods to get StateTimeSeries from StateVector
Spectrogram.is_compatible: used numpy.isclose

    - isclose allows precision differences in sample_rates
spectrogram.spectrogram: multiprocess specgrams

    - use multiprocessing analogous to frame reading to speed up
      Spectrogram generation from a TimeSeries
TimeSeries.spectrogram: use spectrogram.from_timeseries

    - use new (optionally, default not) multiprocesses spectrogram
      generation routines