Consider change in version policy to have unique artifacts

[wglasshusain]

When upgrading from 0.8-2 to 0.8-3 I encountered a regression problem (see issue #3).

Unfortunately, I am not able to easily revert to an earlier version. This is because the files are stored in luarocks with the same name, regardless of the minor version. From the rockspec:

url = "https://github.com/Olivine-Labs/resty-mongol/archive/v0.8.tar.gz",

I believe the rational is that if the API doesn't change with a minor version, then there's no reason to not have the latest. But it'd be better if we could control which version we are using (especially for cases like this with regression errors).

I recommend the project switch to unique artifacts for each release. Just something to consider.