updated look and feel

[eddelbuettel]

Various:

• [x] New font
• [x] New color scheme for title and headers
• [x] Equation number update
• [x] Small other edits
• [x] Updates in skeleton.Rmd (such as a two-column figures)

[eddelbuettel]

Done in d430cd852ec8b626a6a071a8e2123f551421f4c1