Fix for multiple ranges in a row

Some row has two ranges in spans, for example:
  <row ... spans="1:10 6802:6802">

This xlsx file causes following panic:
  panic: Invalid range (not integer in upper bound) 1:10 6802:6802

Changes:
 * Call makeRowFromRaw instead of makeRowFromSpan
   when spans has 0 or 2 or more ":"
Merge branch 'fix/xlsx-multiple-spans' of https://github.com/minimum2scp/xlsx into minimum2scp-fix/xlsx-multiple-spans
Add unit test for support for multiple spans in a row.
go fmt
Merge branch 'minimum2scp-fix/xlsx-multiple-spans'