Start adding support for runtime errors:

- Primitives can now signal an error.
- An error prints a callstack and ends the current (and right 
  now only) fiber.
- Arithmetic operators error if the operand is not a number.
- Real error for method not found.
- Associate source file name, and method names with functions.
- Debug line number info for functions.

Unfortunately, this regresses perf on fib about 15%, mostly
because of the better checking in arithmetic ops.

There's still a bunch of clean up to do, but this is a big step
in the right direction.

test/method/not_found.wren

@@ -0,0 +1,3 @@
+class Foo {}
+
+(new Foo).someUnknownMethod // expect runtime error: Receiver does not implement method 'someUnknownMethod'.

test/number/divide_wrong_argument_type.wren

@@ -0,0 +1 @@
+1 / false // expect runtime error: TypeError: Right operand must be Num.

test/number/minus_wrong_argument_type.wren

@@ -0,0 +1 @@
+1 - false // expect runtime error: TypeError: Right operand must be Num.

test/number/mod_wrong_argument_type.wren

@@ -0,0 +1 @@
+1 % false // expect runtime error: TypeError: Right operand must be Num.

test/number/multiply_wrong_argument_type.wren

@@ -0,0 +1 @@
+1 * false // expect runtime error: TypeError: Right operand must be Num.

test/number/plus_wrong_argument_type.wren

@@ -0,0 +1,3 @@
+1 + false // expect runtime error: TypeError: Right operand must be Num.
+
+// TODO: What about a string on the RHS?