fix for move_to_child_with_index method

when moving a node downward (but not to the bottom) within its current parent the
`move_to_child_with_index` method would insert the node in the wrong place.

This is because when moving a node downward the positioning needs to take into account the fact
that the moving node is being removed from its current position.

also, add code to handle a no-op call -- moving a node to the position it's already at -- w/o raising an error.
Merge pull request #268 from jordan-brough/fix-for-move_to_child_with_index

fix for move_to_child_with_index method
Fixes #270
Update README
Update changelog
Prep gem version 3.0.0
Been way too long since we had a gem release.
Maybe this will prompt us to do it more often.
Fix bug in Rakefile
We don't need sudo in CI
Cache bundler on CI
Updated rspec to 3.x
properly destroy objects when called from associated object.
Merge pull request #278 from kuldeepaggarwal/fix-#162

properly destroy objects when called from associated object.
Set version to 3.0.1
Merge master