Merge pull request #9 from rdocking/master

Fix typo 'classis' to 'classic'
Edit seminar 08 methylation
Add link to PDF slides for lecture 15 re: Principal Components Analysis (PCA)
Link to seminar08_methylation; many small wording and code changes

WARNING: Does not compile nicely when I run my automated website build function. A manual walk-through went fine, so will require some troubleshooting. Posting anyway to facilitate today’s seminar.
Create subdirectories for hw01 and hw02 within homework. Fixes #10.
Edit links to reflect new subdirectories for hw01 and hw02 within homework. See #10.