Update the CONTRIBUTING section of the README and provide a CONTRIBUTING file.
Add tests for Node::all() when using it with soft deletes.
Fix check for 'Node->storeNewParent()'. Fixes #79 and closes #81.

This will avoid moving the node when setting 'parent_id' to null and node is already root.
Merge branch 'fix-nullify-parents' into develop
Add pessimistic locking. Closes #89.

Use pessimistic locks when performing certain operations which
may result in a race condition. Mainly:

+ When moving nodes (updates bounds and depth for whole subbranches).

+ While looking for rightmost node (at every node creation) which may
result in some error, mainly if it gets updated while doing this.

+ When pruning whole subtrees.
Merge branch 'add-row-locks' into develop
Updated .gitignore and added .gitattributes
Travis improvements
Removed unneeded .gitkeep file
Add some missing files into .gitattributes
Merge branch 'GrahamCampbell-git' into develop
Merge branch 'GrahamCampbell-travis' into develop
Merge branch 'GrahamCampbell-gitkeep' into develop
Rename 'isValid' static method. Fixes #93.

Rename 'isValid' method to 'isValidNestedSet' to avoid name clashes with validator packages.
Add 'force' option to rebuild operations.

This will force the index rebuilding process even if the underlying nested set structure is valid.
Change 'makeRoot' implementation.

Moving to a root node now promotes the provided instance to be the rightmost root in the tree, thus being more consistent. We are no longer moving the current subtree to the right of the first available root.
Implement trunks family of methods. Closes #59.

Implement 'allTrunks', 'trunks' and 'isTrunk' methods to complement the leaf and root ones. We consider a trunk a node which falls in the middle of a branch (not root and not leaf).
Remove unneeded check on soft deletes test.
Touch all nodes involved in a move operation.

Because of a previous impl change, the nodes involved in a move operation would not get 'touched'. Baum will now update the 'updated_at' field manually if it is used in the base model.
Update CHANGELOG & bump version.