Modify schema to include support for larger decreases

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The current schema supports single and double decreases in the form of k2tog
and k3tog or skp stitches for example. Functionality for larger decreases is
necessary because lace patterns routinely decrease in larger groups.

This will probably end up looking like:

<multiple-decrease number="8" yarn-idref="yarn1"/>

There isn't a need for a "type" right (i.e. ssk, k2tog, etc.)? Anything past a 
double decrease is essentially a knit-n-together or can be expressed in atomic 
operations?

Moved from http://www.doublebock.net/bugzilla/show_bug.cgi?id=22

Original issue reported on code.google.com by [email protected] on 3 Nov 2011 at 3:13