Preparing to release v1.6.1

Added Template.Render() overload which takes in a Stream, and corresp…

…onding unit test

Added strongly named key to DotLiquid assembly, meaning it can now be…

… deployed in the GAC.

The .snk file is part of the repository; because anybody is able to create "official" builds, it's up to users to get binaries from the official places.

Added overloads to all Template.Render* functions to take in a stream…

…, in addition to the existing versions that returned a string.

Modified build script to also generate NuGet package

Matches with v1.0.0 of NuGet package