Merge pull request #58 from achernyak/master

Fixed the missing "/" in sheets
Output Cols.
Copy in column definitions from XLSX files, expanding them into one definition
per row as we go.  Also exclude definitions for columns outside the dimensions
of the spreadsheet.
Use zero index for <col> min and max.
Go back to 1 based column indexing.
fixes #53 (files produced need repair)

The problem was that when we build the final object tree for marshalling
in XML, we use make([]Col, MaxCell) and then use append on the resulting
array. This has the undesired effect of initializing an array with a
number of empty cells and then appending to that array. The result is that
the final XML contains a bunch of empty column definitions before the
real columns start.
Merge pull request #60 from ilowe/master

fixes #53 (files produced need repair)