ODS import and improved export. XLSX support with new xlrd version.

ODS `detect`, `import_set` and `import_book` added 
Edited `dset_sheet` to write float numbers in the right format 
Also included smaller changes and older pull requests, since they have not been included in the newest version 
Use newest <a href="https://pypi.python.org/pypi/xlrd">xlrd</a> version. It can import both XLS and XLSX.