Add struct and type doc comments for extra::url::*
Add struct and type doc comments for extra::url::*

Updated doc comments further, following suggestions from huonw in PR
#10752.
Search for libfoo.a on windows as well as foo.lib

Turns out LLVM only builds libfoo.a libraries, so we're going to need this logic
to statically link librustc
auto merge of #10752 : dhodder/rust/master, r=pcwalton
auto merge of #10785 : alexcrichton/rust/omg-i-hate-windows, r=pcwalton

Turns out LLVM only builds libfoo.a libraries, so we're going to need this logic
to statically link librustc