adjustments to responsive resizing

Trying for more consistency in image sizing as well as better
padding/margins at smaller viewports.
slight adjustments for tiny screens

- Phones are computers too.
- This narrows the padding on <30em views, which makes for a slightly
wider typographic measure.
- New 22em media query in place of 25em media query
Merge branch 'master' into responsive-standard-scaling
.excerpt-index bug at 2 column (44em) width

I forgot to keep the width for the index at 42em when changing the
.page width to 36em.
consistent size for .site-nav at >44em

Previously declared >50em
Merge pull request #45 from opattison/responsive-standard-scaling

better responsive scaling with some adjustments to typographic measure
Merge branch 'master' into image-post