Add version-specific install scripts.

I don't know anything about these `.tt` files or ASP, so this seemed the quickest / easiest way. I only went back to `1.7` because the other scripts don't take into account the `uname` info. 

My desire to have version-specific install scripts is because I am creating a Docker container and installing Nix within that container. The curl-style install is very convenient in a Docker situation. Unfortunately, `RUN` commands in Docker are cached if they don't change, so the command to install nix won't update even if nix has. However, if I hardcode the version in the install, then I can update the `RUN` command when nix's version is updated.