large breakpoint change, excerpt index scaling enhancements

Biggest breakpoint is no longer a common 90em (1440px) but a less
common "in-between" value of 95em. This prevents unncessary transitions
at typical large screen sizes (for example: laptops that have
full-screen 1440px viewports). Another change is that at larger screen
sizes, the excerpt items just scale up at 1.125 to 1.25 at larger
screen sizes rather than change proportion. The excerpts were looking
too small at 1x scaling on big screens, especially since the articles
associated with them would scale up to 1.5x at the largest viewports
(90em+).
Merge pull request #37 from opattison/excerpt-scaling

large breakpoint change, excerpt index scaling enhancements (resolves #35)