Added extract-text and tweaked webpack config creation

[smashingpat]

I have added some tweaks to the webpack config creation so it becomes a bit more consistent and extendable.

• instead of webpackConfig it becomes createWebpackConfig to create one
• createConfig parameter minify changed to options and it expects an object with options (including minify). The boolean method still works but added a deprecation message for later versions.
• added extract-text-webpack-plugin so the css will be written in its own css file, can be disabled in the createConfig by settings the option cssInjection to true (see example below on implementation)
• entry and output parameters must be relative paths, added an assert with a throw Error

const { createConfig, createCompiler, createBuildTask } = require('meister-gulp-webpack-tasks');

const webpackConfig = createConfig('./example/main.js', './dist/hello.js', {
    minify: true,
    cssInjection: true,
});

const startBuild = createBuildTask(createCompiler(webpackConfig));

startBuild();

[Thomasvdam]

Uh oh