contain icon, offset feature

[dangreen]

Source:

Before:

After:

After with offset:

Now you can set offset (in percents) in config, example:

let config = {
    background: "#0030d9",
    logging: true, 
    online: false,
    icons: {
        android:      false, // Create Android homescreen icon. `boolean`
        appleIcon:    { offset: 30 }, // Create Apple touch icons. `boolean`
        appleStartup: false, // Create Apple startup images. `boolean`
        firefox:      false, // Create Firefox OS icons. `boolean`
        windows:      false, // Create Windows 8 tile icons. `boolean`
        coast:        { offset: 30 },  // Create Opera Coast icon. `boolean`
        favicons:     true,  // Create regular favicons. `boolean`
        yandex:       true   // Create Yandex browser icon. `boolean`
    }
};

[haydenbleasel]

Can you tighten this up into one line please?

[haydenbleasel]

Awesome PR, can you check the comment I just dropped?

Also, we're going to need README updates.

[haydenbleasel]

Great stuff 👍 Just waiting for Travis then I'll merge.