Merge pull request #508 from tshort/master

More cleanups for #490 - remove more index grouping code.
Convert to using symbols for column names.
Merge pull request #509 from tshort/symbol-column-names

Convert to using only symbols for column names.
No peeking (in readtable)
Add readnrows! methods for faster parsing
Merge pull request #513 from garborg/readtable

Speed up readtable
Add append function
Stop exporting some names
Add deprecation warnings for #509
Make tests pass
Make io.jl tests run from any directory
Clean up show re. strings and symbols
Determine io settings from file extension
Merge pull request #521 from garborg/master

Better use file extensions in readtable and writetable
Merge pull request #522 from JuliaStats/jmw/newshow

Clean up show re. strings and symbols
Add join tests, get them passing
Make RDA.jl tests run from any directory
Merge pull request #524 from garborg/join

Update join
Add deprecation warnings for getindex(::AbstractIndex, ::String)

Fixes #525
Quick fix for formula bug