Switch to creating style information, for every cell, as we go, instead of
doing this on demand, this makes styles symmetric for read write purposes,
though still Cell oriented in the public UI.
Add Fill data to TestMakeXLSXStyleElements.
Add border information to TestMakeXLSXStyleElements.
Remove placeholder comment
Merge pull request #60 from ilowe/master

fixes #53 (files produced need repair)
Tests style elements getting added into the styles.
Set CellStyleXf FontId, FillId and BorderId.
Set font, fill and border ids on CellXf.
Every cell has a linked style.
- Add ApplyBorder, ApplyFill and ApplyFont to user oriented Style struct.
- Coppy these booleans back when making XLSX elements.
Test that we copy the ApplyBorder, ApplyFill and ApplyFont attributes from the
CellXf and CellStyleXf into the user oriented style.
Add a couple of docstrings.
Merge branch 'output-styles'
Resolve failing test post merge from output-styles (cols were not present in split styles expectation).
Merge branch 'master' of github.com:tealeg/xlsx
Resolve failing tests from merge.