Split generic methods into SorterBase
Sorter now extends IterableSorter which sorts but doesn't write
Provides Iterator but is not Iterable
Basic test
Implement Closeable
Restore previous APIs for compatibility
Merge pull request #10 from nathanlws/iterable-sorter

Sounds good -- I may do minor tweaks after merge.
Minor refactored wrt #10, update release notes
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[maven-release-plugin] prepare release java-merge-sort-0.9.0
[maven-release-plugin] prepare for next development iteration
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