return the original obj in _.each. closes #1391
Test return value of _.each.
Merge pull request #1429 from braddunbar/each-test

Test return value of _.each.
fixes #349: add _.partition function
document _.partition
Merge pull request #1430 from jashkenas/GH-349

fixes #349: add _.partition function
simplify _.partition documentation example
each chaining docs