Added explicit manipulators to InchCoord & InchLocation

Now InchCoord's doubleValue property and nsValue representation, and InchLocation's x and y properties and cgPointValue representation


• Added DoubleManipulatorBlock and NSNumberManipulatorBlock block types to InchCoord, and CGPointManipulatorBlock to InchLocation.
	» All take and return the type in the name except for NSNumberManipulatorBlock which takes a higher-order NSDecimalNumber and returns an NSNumber.  The argument type is also const-ed, but I'm not sure Obj-C enforces that.
• Added manipulateAsDouble: and manipulateAsNSNumber: methods to InchCoord and manipulateAsCGPoint: to InchLocation.
	» These allow manipulation via a block, which _should_ make it clear that setting a value is non-trivial and not what you normally want to do.  I guess we'll see how these persist.
	» InchCoord#manipulateAsNSNumber: and InchLocation#manipulateAsCGPoint use manipulateAsDouble: internally (the latter once for each coord), which is awesome and keeps things DRY.
• Updated sets in InchLocationTests and InchCoordProxyTests to use the new manipulators.
	» The manipulators are perfect for this use-case, when we just need to set a value with no