Abstract out magic number in code
Added comment for date parser
Added more comment for command parser
Description for command and param enum
Move hash constant value out
Added comment for interval earch
More comment for command object
Method for clear all completed
Merge branch 'master' of github.com:cs2103aug2014-w13-4j/main
Added clear command to command enum
Storage now supports get all completed tasks
Register get all completed task to storage
Added clear function to logic
Set clear as one of the logic api
Modify Histroy model to support a single action that result in a list of task to change
Corresponding change to logic undo
Add list support to the undo function in logic
Clear command now can be undone
Merge branch 'master' of github.com:cs2103aug2014-w13-4j/main into pn-clear-all

Conflicts:
	src/logic/Logic.java
Merge branch 'master' of github.com:cs2103aug2014-w13-4j/main