Changed property definition to 'copy', removed explicit setter methods for inputBlock and outputBlock

Since the setter and getter methods `-(void)setInputBlock:` and `-(void)setOutputBlock:` are basically implementing the automatically generated 'copy' manually, as far as I can see there is no reason not to change the properties for inputBlock and outputBlock to "copy" (from "retain") and remove the manual setters.

The downsides: none I can see.
The upsides: two less warnings at compile time.

Re: issue #3 Warnings and Link Errors