Adds new multi-fetch functionality

The Bucket interface and DomainBucket are now capable of
returning / using a new MultiFetchObject that will parallelize
a set of fetch operations using a threadpool and return a
list of futures.
Fixed getMaximumPoolSize() removed ifModified()

getMaximumPoolSize was erroniously returning the corePoolSize and
ifModified(VClock vclock) is not applicable to a multi-fetch.
Fixed typos, copyright, added usage example

Also removed get/set MaximumPoolSize as it has no effect with
an unbounded work queue - only corePoolSize is considered.
Merge pull request #225 from basho/add_multi_get

Adds new multi-fetch functionality