Clean up uniques when deleting

A bug in the test where the key "unique" was used 
instead of "uniques" meant the test 
"removes the previous index when deleting" was
passing when it was in fact failing. Model.delete 
now mirrors Model.save in how it cleans up indexes
and uniques.
Add missing changelog entry.
Performance: Make Collection#each retrieve objects in batches.
Add changelog entry for 33fa712432841e0b3a530433917ac69d651737d9.

Intentionally making this two commits in order to make cherry picking
easier.
Merge pull request #86 from damonmorgan/bug/delete_unique

Clean up uniques when deleting
Avoid checking for existence in Model.with (@djanowski)

Conflicts:

	lib/ohm.rb
Bugfix release.
Fix link to Transactions topic on redis.io

Signed-off-by: Michel Martens <michel@soveran.com>
Bring up to date the chaining example
Delete Ohm::Model::Validations#assert_unique reference

This method seems to not exist anymore, deleting it from
the documentation.
Cleanup test suite for ruby 2.0.
Merge pull request #102 from frodsan/remove_ruby_2_0_warning

Remove Ruby 2.0 warning. Use `to_enum` instead of `Enumerator.new` without a block.
Update CHANGELOG. Ohm 1.3.2 was released 8 months ago.
Merge pull request #112 from frodsan/update_changelog

Update CHANGELOG. Ohm 1.3.2 was released 8 months ago.
Merge pull request #87 from kevinjhanna/update-chaining-example

Bring up to date the chaining example
Merge branch 'master' into v2