Add rust-gdbgui script.
Add rust-gdbgui script.

This script invokes the gdbgui graphical GDB front-end
with the Rust pretty printers loaded. The script does not install
gdbgui, that must be done manually.

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