Support for merged cells

[nlarusstone]

Thanks for the library -- it's great to have a performant binding.

One major feature of spreadsheets is merged cells, which calamine added support for earlier this year: tafia/calamine#437

Do you have any plans to support merged cells in the python bindings?

If not, would you be open to a contribution here?

[dimastbk]

If not, would you be open to a contribution here?

Hi. Yes, PR welcome.

[WenbinHou]

+1 for this

[leon49]

+1 for this

[cprevosteau]

+1 for this

[rockswang]

Please create a new release with the latest code, as the currently pip-installed version 0.3.2 still does not include this fix (i.e., retrieving merged cell information).