Most object types get their own file now

This is hopefully going to make navigating the source tree easier.
Hopefully.

The only types that don't get their own files are:

* function types (UserFunction, BuiltinFunction, Method), which all live
  in obj/function.rs
* Nil, which lives in obj.rs
* Obj, which lives in obj.rs

Type definitions and init_types now live in obj/ty.rs.

New obj::prelude module for common imports.

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

src/obj/bool.rs

@@ -0,0 +1,77 @@
+use std::fmt::{self, Debug, Display};
+
+use gc::{Finalize, Trace};
+
+use crate::obj::macros::*;
+use crate::obj::prelude::*;
+use crate::obj::BaseObj;
+use crate::vm::Vm;
+
+#[derive(Trace, Finalize)]
+pub struct Bool {
+    base: BaseObj,
+    bool_value: bool,
+}
+
+impl Bool {
+    pub fn new(bool_value: bool) -> Self {
+        Self {
+            bool_value,
+            base: Default::default(),
+        }
+    }
+
+    impl_create!(bool_value: bool);
+
+    pub fn bool_value(&self) -> bool {
+        self.bool_value
+    }
+}
+
+impl Display for Bool {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "{}", self.bool_value)
+    }
+}
+
+impl Debug for Bool {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "{}", self.bool_value)
+    }
+}
+
+impl Object for Bool {
+    fn is_truthy(&self) -> bool {
+        self.bool_value
+    }
+
+    fn equals(&self, other: &dyn Object) -> bool {
+        if let Some(other) = other.as_any().downcast_ref::<Bool>() {
+            self.bool_value == other.bool_value
+        } else {
+            false
+        }
+    }
+
+    impl_base_obj!(Bool);
+}
+
+impl Bool {
+    impl_do_call!(to_bool);
+
+    pub(crate) fn init(_vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        // This is a no-op. We don't want the user-exposed `__init__` function to do anything,
+        // instantiation is done in the `__call__` function.
+        FunctionResult::ReturnPush(Nil::create())
+    }
+
+    pub(crate) fn to_int(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let bool_value = with_obj_downcast(vm.frame_stack()[0].clone(), Bool::bool_value);
+        Int::create(bool_value as i64).into()
+    }
+
+    pub(crate) fn to_float(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let bool_value = with_obj_downcast(vm.frame_stack()[0].clone(), Bool::bool_value);
+        Float::create(bool_value as i64 as f64).into()
+    }
+}