Merge pull request #78 from sun-rui/master

Fix a bug that modifications to build.sbt won't trigger rebuilding.
Fix syntax error in examples/kmeans.R.
Adjust coding style.
Merge pull request #79 from sun-rui/fix-kmeans

Fix syntax error in examples/kmeans.R.
Add mapPartitions() method to RDD for API consistency.
Update Rd file and add a test case for mapPartitions.