Don't duplicate Xf's in the style file.
Use 1/0 instead of true/false.
Default the font.
Copy old styles across, when restyling a car.
Test xlsxFill.Equals
Test xlsxBorder.Equals
Write File to io.Writer
Test xlsxXf.Equals.
Merge pull request #67 from M1rt/master

Write File to io.Writer
Merge branch 'master' of github.com:tealeg/xlsx
Merge pull request #2 from tealeg/master

mearge