excel, build: Pin xlwings wersion to 0.2.3 (0.3.0 broken!!).

- excel: Add utility funcs to open or get current Workbook, when run from python.
-- FIX not to add empty sheets when overwritting existing ones.
- core: Remove __init__ from cycles package.
- docs: CHANGES mention broken behavior on speed-down to a halt.
-- README improve project's coordinates on landing page.
-- TRY fixing RTD build from http://blog.rtwilson.com/how-to-make-your-sphinx-documentation-compile-with-readthedocs-when-youre-using-numpy-and-scipy/.
- ci: FIX py27 failing on setup.py reading ver with unicode.