Missing Types in Value.cs

This is an issue that arises when assigning values to the global variable state from code in Unity.
I was getting the following error when trying to assign values in the variable state to zero: `StoryException: Invalid value passed to VariableState: 0`
I noticed that it only occurred when I tried to assign it to uint zero, but not int zero. After some digging I found that uint isn't included in the type checks in `Runtime.Value.Create`. I'm just casting to int for now, but it would be great to have uints included in the type checks.
**TLDR**
Works: `story.variablesState["myVar"] = (int)1;`
Doesn't work: `story.variablesState["myVar"] = (uint)1;`

Thank you for all your work, I love Ink!