Merge branch '3.0' of github.com:cakephp/docs into 3.0
Merge branch '3.0' of github.com:cakephp/docs into 3.0
Adding docs for collection sortBy
Fixing typo
fixed rst syntax
Merge pull request #978 from okonomi/3.0-migration-guide-syntax-fix

Fix rst syntax in 3.0 migration guide
Merge pull request #976 from cakephp/3.0-collection-sorting

3.0 collection sorting
Adding docs for other colleciton methods
Fixed problmes found in review
Fixing derp
Merge pull request #977 from cakephp/3.0-other-collection-methods

3.0 other collection methods
Add content to the collections.filtering section.
Adding example for using `on` with a closure in the validator
Fix incorrect key.
Merge pull request #979 from cakephp/3.0-optional-validation

3.0 optional validation
Add additional example and class anchor.
Merge pull request #980 from cakephp/3.0-collection-pt2

3.0 collection filtering