RFE Engineering notation: support multiple of three exponent inscientific notation

["efa@iol.it" <efa@iol.it>]

hi,
a propose a RFE, the Engineering notation.
Can be supported with a multiple of three exponent in current scientific 
notation.

I propose to add the attribute:
number:exponent-multiple
to the element:
<number:scientific-number>

This resolve the problem of implementation dependant formatting of OpenOffice, 
LibreOffice and other spreadsheet.


Another desired format customization is the accuracy, to be used as 
alternative to:
number:decimal-places (and combined with number:min-integer-digits), meaning 
the number of significative digits, before and after the decimal dot.
I propose to add the attribute:
number:accuracy
to the element:
<number:scientific-number>


References:
http://www.openoffice.org/issues/show_bug.cgi?id=5930
https://bugs.freedesktop.org/show_bug.cgi?id=30716


thank you in advance,
Valerio