rustdoc: Style of [src] link for trait implementors
rustdoc: Style of [src] link for trait implementors

A change suggested by @GuillaumeGomez and @QuietMisdreavus.

Also slight reindenting of the appropriate CSS section.

GBGamer/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust