remove extraneous npartitions attribute on BlockingStrategy
provide convenience methods to generate SimpleBlockingStrategy instances
add calcAvgSize method to BlockingStrategy, simplify generateFromBlockSize factory args
add print-based warning about large blocks - plan is to convert print to logging in future
add Images.toSeries and Images.saveAsBinarySeries methods
add default value to blockSizeSpec parameter
add default blockSizeSpec to toBlocks method, missed in last commit
Merge pull request #71 from industrial-sloth/new_imageblocks

New imageblocks: simplify blocking strategy creation