Support aliases

We should be able to use convert-tsconfig-paths-to-webpack-aliases to parse aliases from tsconfig.json, then add those to Webpack's resolve.alias config option.

The primary hurdle with this will be finding the tsconfig.json. I suppose it's probably easiest to allow specifying its location as a config option. afe76a61 added code for locating the tsconfig, so implementing this is almost trivial now.

Note: if this is especially important to someone, please leave a comment, then I'll bump its priority.