Read in styles, support for merged cells, header/footer support.
Created originally on Bitbucket by Adam Morris
Added a pull request that brings in support for readings styles, merged cells etc. It seems to be working well - I've tested with a number of local files, as well as writing an excel file with openpyxl, reading it back and and re-saving it, and have resolved all the issues that have been found.
It grew a bit larger than I'd started with so I'm not sure if it's the best way to implement each component, or if the pull request is the best way to merge the changes in. If there is anything I can do to improve / re-work this, please do let me know.