Allow search of local images

[rheinwein]

Since .search queries only the Docker Index, it would be helpful to have a method that will also search through local images. You can retrieve all local images via Docker::Images.all and match a query from that data set, but it would be nice to push that functionality up into the API rather than rolling our own.

[bfulton]

@rheinwein sounds like that could be a nice convenience method to add. Want to take a stab at it?

[rheinwein]

@bfulton For sure.