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/float.npp

@@ -128,3 +128,12 @@ println(-0.0)
 println(--0.0)
 println(---0.0)
 
+# constructor
+println("constructor")
+println(Float("10"))
+println(Float("10e3"))
+println(Float("12e-3"))
+println(Float(1234))
+println(Float(1.5))
+println(Float(true))
+println(Float(false))