setup.py: copied setup infrastructure from GWpy
setup.py: restore share/ file install
PlotList: deleted unused class
docs: make into /build/sphinx

    - matches default from python setup.py build_sphinx
config.py: added method to convert ConfigParser

    - from_configparser will convert ConfigParser to GWSummConfigParser
      subclass
    - added InterpolationMissingOptionError (not in
      configparser.__all__)
gw_summary: don't require [states] or [html]

    - now handles missing sections gracefully
plot.registry: allow non strings in register_plot
state.registry: improve docs, add get_states
state: improve docs, etc
config: preserve case in INI files
plot: renamed classes, improved documentation
tabs: multiple combined improvements

    - mainly documentation improvements
    - one or two bug fixes
Makefile: remove _generated with make clean
docs: improved documentation