Merge pull request #232 from kmsquire/endof_GroupedDataFrame

Added endof(g::GroupedDataFrame)
Merge pull request #231 from kmsquire/SubDataFrame_setindex

Added setindex! for SubDataFrames
Add a kwarg constructor for DataFrames (#228)
Example: DataFrame(x = [1:4], y = rand(4))
Merge branch 'master' of git://github.com/HarlanH/DataFrames.jl
Changed replace_names => rename
Added rename!() using Dictionary, function (ala Pandas)
Index updates

* Define show, showall for Index
* Fix: rename! needs to return the modified Index for rename to work
* Added pop!, shift!, unshift!, append!, prepend!
* Fix: delete! should return the deleted item (for parity with mainline julia, use by pop!, unshift!)
* Fix: push! should return the modified Index (for parity with mainline julia)
* Added tests for the above