renamed xlwings.py to main.py and changed to abs imports
first steps towards mac support
factored out GetObject call and renamed global wb and fixed __repr__ of Range object
implemented Workbook __init__ crossplatform except active_sheet
refactored ActiveSheet on windows
implemented ActiveSheet on Mac
added TODO
implemented Range __init__ crossplatform
implemented crossplatform Range value property
This resolves Issue #41 (string issue with MultiHeader DataFrames)
changed imports again (absolute/relative)
fixed a few windows bugs that were introduced during the cross-platform implementation of the value property
implemented Workbook.activate() cross-platform
corrected cell addresses by dropping "range"
implemented Workbook.close() crossplatform
implemented Workbook.get_selection() and Range __repr__ crossplatform
moved version string into __init__
implemented Workbook.clear and clear_contents cross-platform
implemented Range.formula property cross-platform
implemented Range.vertical property cross-platform