[1.0] Can't use local plugins

[rstacruz]

There doesn't seem to be a way to use plugins that are stored in the project's repository itself.

// gatsby-config.js
module.exports = {
  plugins: [
    'gatsby-source-filesystem',
    'gatsby-transformer-sharp',

    // Let's try to load our own custom plugin
    // Relative path?
    './lib/my-gatsby-custom-plugin', // nope

    // Relative path in an object?
    { resolve: './lib/my-gatsby-custom-plugin' }, // nope

    // Absolute paths?
    require.resolve('./lib/my-gatsby-custom-plugin'), // nope
    { resolve: require.resolve('./lib/my-gatsby-custom-plugin') }, // nope
    '/absolute/path/to/plugin.js', // nope

    // Paths that are directories?
    '/absolute/path/to/plugin/', // nope
    '/absolute/path/to/plugin', // nope
    { resolve: '/absolute/path/to/plugin' }, // nope
  ]
}

Can I suggest this as a feature? Of course it needs a package.json as well, but that doesn't seem to be such a bad idea.

[0x80]

This is being worked on already #1126

[KyleAMathews]

Would love your thoughts @rstacruz on the design in #1126! Closing this issue in favor of that one.