link-rs.sh: use only -l options for library names

pkg-config might also output -L options.
pass LINK_ARGS directly to rustc

The translation of LINK_ARGS to link.rs is lossy, since it doesn't include -L
options. The user will have to pass the missing link args when compiling a
project that uses glfw-rs, but at least building glfw-rs itself will work.
pass LINK_ARGS to rustc for the examples
Merge pull request #108 from rlane/link-path

support link paths with the recent build changes