Added propper exception handling for computations (not fully done yet as I have some neat ideas)

* Added exception handling to computations.
* Added some much needed comments to stuff (more will come).
+ Added a computation cookie that curently is only used to handle
exceptions but the idea is to provide object that could go and collect
some data and possibly set some internals and then go back to the caller
with that juicy info but that's to be implemented :P