Reorganize main stylesheet sass partials

Use `modules` folder for partials, put _helpers into `global`
Use “base” instead of “global” for SASS structure
Switch to redcarpet for markdown processing

Redcarpet2 seems like a good combination of features that I like, plus
then we can remove all the kramdown config
Add nowrap to contact info and use explicit <br>s

Using two spaces at the end of a line for line breaks seems too subtle
when there is already inline html.
Optimize webfont embedding/inclusion (performance)

Break web font logic out into a partial (easy to override in the Marked
version of Pesto), switch to optimized local versions of font from
Google, embed only regular 300, 400, 700 (no italics, no monospace) and
fetch rest with Google webfont import
Improve font sizing logic + break into a partial

Use variables for widths where font sizes change, increase base
(mobile) font size by 1px, add comments, make print version more precise
Use mobile-first with body font-weight
Improve list and ul bullet styles

At narrow widths, lists are aligned with text with bullet in gutter;
bullet dimensions are defined more precisely; regular indentation
reduced from 2rem → 1.5rem
Latest compiled Pesto css (so much lighter!)