add Str2Date func to handler date cell
Merge branch 'master' of https://github.com/lunny/xlsx into lunny-master
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 ":"
fix GetStyle() 0-origin-start and applyXxxx ignored
Rework date.go to be legible (as far as possible) and add tests.
Return NumberFormat string from Cell.
Test built-in numeric formats.
Merge branch 'lunny-master' with a lot of modification and testing.
Merge branch 'master' of github.com:tealeg/xlsx
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'
Merge branch 'fix-styleindex-0-origin' of https://github.com/nazo/xlsx into nazo-fix-styleindex-0-origin
Merge branch 'nazo-fix-styleindex-0-origin'