[type]fix problem
[Module]Sem
[what]add calling uOS_SemInit in uOS_Start.
[feature] priority bitmap schedule algorithm
[fix problem]
    uOS_EventPost will error, when wait list is empty.
[what]
    1. add waitTaskNum in EventControlBlock.
    2. check if waitTaskNum is 0 in uOS_EventPost, if waitTaskNum > 0,
    then wake task.