Add 'dot' can-set prop to make Mongo style property queries easy

[nlundquist]

As discussed in donejs/donejs#900 MongoDB gives special significance to queries where a nested object is provided, this does a match against the entire nested object rather match against the individual properties of the nested object.

To match against the individual properties of a nested object you have to pass query parameters using 'dot notation' i.e {"address.city":"Chicago"} instead of {address:{city:"Chicago"}}. To support this in can-set you need to add a set comparator for each nested property you query like this. This comparator has to pick the specified nested property out of the set member and do a comparison to the query parameter without assuming which argument will be the query parameter and which will be the set member.

To make adding comparators like that easy we'll be adding a new can-set prop set.prop.dot to be used like:

[phillipskevin]

Should we call this dotNotation? I think it might make it a little more clear thanset.props.dot.

[nlundquist]

Released in can-set 1.2.0