Modified the dynamic programming part

	1. The task length is all integers of timestamp.
	   The timestamp is assumed to be 0.1.
	   For example: if a task length is 7 at 1.0v, then at 0.8v, its
	   length should be 7/0.8 = 8.75. Then it will be round to 8.8
	   which is 88 timestamp. We always use ceil() in rounding.
	2. We invalidate all dynamic programming table entries for a timestamp
	   that is not possible compelte a set of tasks.
	   For example: we have 2 tasks and 2 speeds:
	   The length of T1 at the 2 speeds are (3, 5) and
	   The length of T2 at the 2 speeds are (4, 7).
	   So the only valid timestamp in the table entries are (7, 9, 10, 12);
	   Other entries are all nonvalid.
Merge branch 'master' of /home/yzhang/EnergySys/simu/constant_power_charging_test