solution for merge-sort project
added my tictactoe sol
Update project_building_blocks.md

Added my solutions
Updating typo in link
Merge pull request #481 from N19270/merge-sort

add my solution for merge-sort project
Merge pull request #482 from ArmanG/patch-7

added my tictactoe sol
Merge pull request #483 from charleszardo/patch-3

Update project_building_blocks.md
Merge pull request #484 from mram1000/patch-2

Updating typo in link