added alloc implementation.
added first free implementation.
Part 3 is Complete

alloc now:
    check if the address pointed by pagedir is valid an allocates a frame for it if not.
    check if address is multiple of frame size.
free now:
    clean the valid flags
Merge pull request #3 from rbkloss/ricardo

Ricardo
Part 4 is Complete

swap:
    check if addresses are valid, mark flags on creating, etc.
Merge pull request #4 from rbkloss/ricardo

Part 4 is Complete
Began to mark point of alteration for part 5.
Merge pull request #5 from rbkloss/ricardo

Began to mark point of alteration for part 5.
Fixed bug added by using ! as bitwise not, bitwise not is   the tilde.
began the implementation of the functions to dump frames to disk·
merging with master