Guide's Mobile version improvement

[sdlins]

Principle: the guide's text should be the king:

Should have more space for the text;

Menu icon on the right up corner takes the entire line space, pushing the title down;

Should have a floating menu icon having the topics;

"Go to top" icon could be smaller and should not stand so over the text;

I don't think the "pencil" edit icon is useful since editions use to be made via PR. It's only one more thing to stands over the text;

At the end of the each topic it should be a next/before topic links;

[yii-bot]

Issue moved to yiisoft/yii2-apidoc#41