Implements search by ID in CommandSearch and Storage
Changes ID of ToDoItem to integer
Fixes change in Storage due to change of ID from String to int
Changes implementation of marking and unmarking in Storage
Finetunes from previous commit on CommandDo
Makes IllegalArgumentException explicit in CommandDelete
Fixes errors in CommandUpdate due to changing of ID system
Merge branch 'master' of https://github.com/cs2103aug2014-w13-2j/main
Starts changing implementation of loading from file
Merge branch 'master' of https://github.com/cs2103aug2014-w13-2j/main
Writes completed items that are very old to completed.txt on loading
Completes implementing archiving of old completed items to completed.txt during initialization
Changes documentation of DataFileReadWrite