Add resize! methods
Merge pull request #99 from garborg/resize

Add resize! methods
Merge pull request #100 from JuliaStats/sjk/typed_literals

Support typed array literals with atsign-data and atsign-pdata
Efficient sorting of DataArrays

This fixes #92, and also speeds up sorting generally, since we avoid
type instability. It also includes a change that places NAs at the end
instead of the beginning of a sorted array, consistent with the way
Base sorts NaN values.
Clean up indexing, take 2

This is a reimplementation getindex/setindex! based on the
implementation in Base. nd indexing now works, as does setting part
of a DataArray to be another DataArray that contains NAs.

Performance of a[1:end] = a[1:end] is roughly 2x Base. I think this
could still be improved by hoisting loads of the fields of the
DataArray/PooledDataArray, but I need to see if that's possible without
making the code substantially more complicated.

Indexing with a DataArray that contains NAs now throws. I removed
some tests that were testing indexing operations that now throw a
BoundsError. (These indexing operations also throw a BoundsError on
Arrays.)
Performance improvements for new indexing implementation

- Extract fields from DataArray and PooledDataArray before looping.
  This avoids checking repeatedly for undefined references.
- Keep the whole pool for getindex for PooledDataArray.
- Faster setindex! for a PooledDataArray into another PooledDataArray.
Fix indexing bugs and add more comprehensive tests
Reorganize indexing functions, remove inline getindex/setindex! docs
One more PooledDataArray optimization
Merge pull request #102 from JuliaStats/sjk/sort

Efficient sorting of DataArrays
Use setindex! to implement append!
Sort NAs to last position for PooledDataArrays as well
Fix and test sorting of PooledDataArrays with unsorted pool

This can be done more efficiently, but working is better than not
working.
Fix reverse sort for PooledDataArrays
Merge pull request #106 from JuliaStats/sjk/pdasort

Sort NAs to last position for PooledDataArrays as well
Merge pull request #104 from JuliaStats/sjk/indexing2

Clean up indexing, take 2
Implement reductions with optional skipna argument