add objective and label
'dict' -> 'dictionary'

for clarity.
fix code spacing
minor fixes

validated some of the code blocks.
explain indexing better

Using loc/iloc is recommended over [] indexing.  It is more explicit,
less error-prone, and more efficient.

csv -> CSV (it's an acronym)
various improvements

use iloc for indexing
use enumerate for ordered list
Merge branch 'develop' into pandas_ian

Conflicts:
	Python/pandas/pandas.tex
Merge pull request #661 from ayr0/pandas_ian

Pandas improvements