Runtime errors should use sourcemaps

[coxmi]

Runtime errors currently display references to the compiled output, rather than the source file.

ReferenceError: undefinedVariable is not defined
    at /Users/michael/Projects/toast-test/dist/test.js:6516:1
    at /Users/michael/Projects/toast-test/dist/test.js:6528:3
    at Object.<anonymous> (/Users/michael/Projects/toast-test/dist/test.js:6531:12)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)
    at /Users/michael/Projects/toast-test/node_modules/toast-static/dist/generate.js:38:89

To do

• Follow path references, and parse sourcemaps to generate easier-to-read errors
• Match webpack output in style