Added rust-empty.mk

To build with rust-empty, type

`make link && make -f rust-empty.mk`
Added docs about rust-empty to README
Moved rust-empty specific gitignores
Merge pull request #173 from bvssvni/master

Added rust-empty.mk
Upgraded to latest Rust
Merge pull request #177 from bvssvni/master

Upgraded to latest Rust
Add unsafe_destructor to fix build
Merge pull request #179 from csherratt/unsafe_destructor

Add unsafe_destructor to fix build
Update for Cargo
Merge pull request #178 from cmr/master

Update for Cargo
Upgraded to latest Rust-Empty
Merge pull request #180 from bvssvni/master

Upgraded to latest Rust-Empty
Rename cargo package name

Use the more idiomatic `glfw` name.
Upgraded to latest Rust-Empty
Merge pull request #181 from bvssvni/master

Upgraded to latest Rust-Empty
Updated for latest Rust (0dfc90a): *const, *mut
Merge pull request #182 from ozkriff/master

Updated for latest Rust (0dfc90a): *const, *mut
Update to latest nightly
Merge pull request #184 from bjz/update

Update to latest nightly
Update for latest Rust (c97f885): crate file names