Refactored GetVariable, added documentation

docs/get.md

@@ -0,0 +1,34 @@
+# get
+
+Gets an existing variable from the environment.
+
+## Parameters
+
+* name (`string`, `instruction`) - The name of the variable to get.
+
+## Return
+
+(`any`) - The value of the variable.
+
+## Exceptions
+
+* `EvaluationException` - If there was an error while evaluating one or more parameters.
+* `TypeException` - If one or more parameters are not of the expected type.
+* `NameException` - If the variable does not exist.
+
+
+## Instruction Example
+
+```json
+{
+  "type": "get",
+  "_": {
+    "name": "foo"
+  }
+}
+```
+
+### Last Updated
+
+Monday, December 29th, 2022.
+Written by [Netkas](https://git.n64.cc/netkas)