Removed colors still in config and documentation

[nkh]

@qindapao I noticed these color definitions in my user config, it's also referred to in the documentation. These colors seem to have been removed from the Cross code, can I remove those definitions?

		cross_element_backgroud => [1, 1, 1],
		cross_filler_background => [1, 0.9, 0.9],
		normal_filler_background => [0, 1, 0],

[qindapao]

@nkh Besides this, the document may need some cleaning in many places.Especially some key bindings.

[qindapao]

@nkh You can get rid of them, there is no place to use them now.