Add Bool builtin type, branches, and some more stuff

* obj::Bool builtin type is used for truthiness and decision-making
* Branches are compiled and seem to be working for basic integer
  comparison
* Updated version of Shredder to what is current as of writing
* CheckTruth VM instruction that will explicitly set the condition flag
* Probably some other stuff

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

Cargo.toml

@@ -27,4 +27,5 @@ once_cell = "1.4.1"
 
 [dependencies.shredder]
 git = "https://github.com/Others/shredder"
+rev = "c71335"
 features = ["nightly-features"]