Rename functions:

coltypes -> types
colnames -> names
clean_colnames! -> cleannames!

Replace use of earliest_common_ancestor with typejoin
Merge pull request #469 from JuliaStats/jmw/dfprops

[WIP] Rename coltypes, colnames and clean_colnames
Implementation of a DataFrame row as a parameterized SubDataFrame
Add Ranges{Int} to SubDataFrame parameterizations, simplify some function signatures
Misc updates to SubDataFrames

* Change EachRow, EachCol -> eachrow, eachcol, to better match
  Base convention for iterators
* Start to use size(df, 1) for nrow(df), size(df, 2) for ncol(df)
Fix sub for SubDataFrames
Update tests for sub-ranges of SubDataFrames