Add more page format support
Fix Page format (DIN) use standard uppercased name
Add utility function: convert cm to dxa
Table Col width in pct are now convert in dxa if tblw is define
Allow per attribut prefix
headerRelation need this:
<w:headerRelation r:id="rId4" w:type="default" />
define attr like this:
make element(tagname, attrinutes={ 'type': 'default',
				   'id': { 'value': 'riD4' , 'prefix': 'r' }})

Conflicts:

	docx/elements.py
Add a default header
example : 'doc.headercontent.append(paragraph("doc title"))'
Add custom style loading from file ( overwrite default template style)
Allow tabs definition for paragraph
example:
p = elements.paragraph(headertext, tabs=[
					{'leader':'none',
                                         'pos':'1024',
                                         'val':'right'},
					])
Typo
Add a default footer