Update memalloc.c

[ReinierMaas]

The previous implementation releases only the last element. The new implementation releases all free elements that are trailing.

Test 1 =>

• make allocations
• remove them FiLo (inverted order of creation)
• the entire heap is returned to system

Test 2 =>

• make allocations
• remove them FiFo (order of creation)
• only the size of the last removed element is returned to system

• with the changes the entire heap is returned to system