Add #displace, with specs and sample
Add displace methods to Dimensions
Use #update_position
Change #displace to #update_position in gui
Merge with master
Fix button specs by removing huge margin and provide error margin

* margin was so huge that width/height went negative, probably
  something we should be aware of/fix in the future - will file
  an issue
* provided an error margin of 1 because of... computers and
  floating point numbers
Add some displace specs to dimensions
Merge pull request #592 from shoes/displace

Add #displace by @wasnotrice :)