Don't do any merging of config values at all

Leave this up to the user; their config file is a JS file and we give
them access to the default config, so they can do as much merging of
defaults as they like.

src/build.js

@@ -1,13 +1,12 @@
 import fs from 'fs'
 import postcss from 'postcss'
 import tailwind from '..'
-import defaultConfig from '../defaultConfig'
 import CleanCSS from 'clean-css'
 
 console.info('Building Tailwind!')
 
 fs.readFile('./css/tailwind.css', (err, css) => {
-  postcss([tailwind(defaultConfig)])
+  postcss([tailwind()])
     .process(css, {
       from: './css/tailwind.css',
       to: './dist/tailwind.css',

src/index.js

@@ -6,7 +6,6 @@ import postcss from 'postcss'
 import stylefmt from 'stylefmt'
 
 import defaultConfig from '../defaultConfig'
-import mergeConfig from './util/mergeConfig'
 
 import substituteResetAtRule from './lib/substituteResetAtRule'
 import evaluateTailwindFunctions from './lib/evaluateTailwindFunctions'
@@ -17,13 +16,11 @@ import substituteResponsiveAtRules from './lib/substituteResponsiveAtRules'
 import substituteScreenAtRules from './lib/substituteScreenAtRules'
 import substituteClassApplyAtRules from './lib/substituteClassApplyAtRules'
 
-const plugin = postcss.plugin('tailwind', (options = {}) => {
-  if (_.isString(options)) {
-    options = require(path.resolve(options))
+const plugin = postcss.plugin('tailwind', (config = defaultConfig) => {
+  if (_.isString(config)) {
+    config = require(path.resolve(config))
   }
 
-  const config = mergeConfig(defaultConfig, options)
-
   return postcss([
     substituteResetAtRule(config),
     evaluateTailwindFunctions(config),