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