Task scheduling improvements

Now the next time that the task will execute doesn't have the acumulated
time of the execution of the task itself.
Bug correction

If the task was found it makes sense to increment the number of task
present on the system? Not sure if this correction is correct... :S
setTask improvement

When we use the setTask method to modify the task status the task will
be immediately executed on the next timer overflow (not when in PAUSED
state). With this correction, when you change the status of the tasks
they will be executed only when scheduled...
Merge pull request #2 from luismaduro/master

Some improvements/corrections