Merge pull request #9 from dmontenegro/master

FD.dom
Modified builtin dfs in module Search.
This builtin imposes Gecode::DFS to Space.
If the Space have solution then updates its GecodeSpace whit the solution find it.
This builtin is still in development.
Changes to support constraint boolean variables.
- Added one, zero and none operations to the boolean variables interface.
- Added the module BoolVar to the virtual machine.
- Changed some methods in GecodeSpace to support the new boolvar implementation.
Merge pull request #10 from miavisa/css

Modified builtin dfs in module Search.
Changed methods for search builtin.
- No need for a loop in the search one builtin.
- Fixed memory leak when updating constraint spaces.
Added built-in for Gecode::element.
Supports 2 finite domain variable and a list of ints (e.g {FD.element X [1 2 3] Z})