Add do_call macro, implement Bool builtins, add tests

* I noticed that `fn call(...)` in all objects was identical, so I made
  a macro for it. This should make things a little easier to read, since
  do_call is about 30 lines a pop.
* Bool has a constructor now, and a to_int and to_float implementations
* Add tests for constructors and add new bool tests

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

tests/int.npp

@@ -123,3 +123,11 @@ println(10 - -20)
 println(-10 - 20)
 println(-10 - -20)
 println(-0xff)
+
+# constructor
+println("constructor")
+println(Int("10"))
+println(Int(1234))
+println(Int(1.5))
+println(Int(true))
+println(Int(false))