build: Refactor to use Duo

My initial goal here was to not require a global installation of
component@1.  I thought about just converting the Makefile to use a
local copy (`node_modules/.bin/component-*`), but made a biased
decision to use Duo (Duo is better).

This patch reopens then closes #1. :p

----

Breakdown of changes:

**Makefile**:

 - rewrite to actually utilise `mtime`, etc
 - use local duo(1) rather than global component(1)
 - add a `node_modules` target

**package.json**:

 - add Duo as a development dep
 - use the `private` flag to prevent accidental publishing

**slant-frame.{css,js}**:

 - rebuild

**.gitignore**:

 - ignore node_modules
Merge pull request #8 from littlstar/refactor/build-with-duo

build: Refactor to use Duo