Changes in v2.0.0

1. Deprecation warning for index.name - it was never used.
2. 80% performance improvement on example data due to faster indexing of groups.
3. Additional tests for malformed data.

Changes in v1.0.1

1. Substantial performance improvements owing to vectorization and data.table call optimization.
2. Automated tests using the testthat package.
3. Cleanup of package directory and administrative files.