Merge pull request #60 from KellyBlack/black_dev

Update for the talk on solving linear systems.
Merge pull request #61 from KellyBlack/black_dev

Updated the discussion on matrix inverses
notes for week8 MWF
notes for week 8 for MWF
Merge pull request #36 from guangmingyao/yao_dev

Yao dev
Updated the talk on determinants and vector space.