Sampe bitmap added.

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branch : 1.8
Refactored to be a bit cleaner.

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Simple renaming.

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rename : openpyxl/sample/chart_gen.py => openpyxl/sample/charts.py
rename : openpyxl/sample/files/charts_gen.xlsx => openpyxl/sample/files/charts.xlsx
Excel seems to count from 1 for drawings and cNvPr seems to need to be more than this. Need to check the spec but both the perl and ruby implementations do something like this.

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Make sure workbook is empty.

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Relationship ids must be unique. Which won’t be the case if either image or chart id is 0.

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test_write refactored to check only the root node.
test_write_rels now takes images into account. This is pretty flaky.

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Corrected sample ids from enumeration.

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Updated sample charts. Works fine on Office for Mac OS but Excel on Windows complains about the drawings but will accept them. Probably need to add validation. The relevant XML files are identical in XML terms.

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branch : 1.8