Minor "else" improvements

- Do not generate s.never to skip Else branch
- Add Display impl to SourcePosition
- Correct SourcePositions pointing to the end of a parsed expr instead of the beginning
- Remove 'true', 'always', 'false' and 'never' from README.md

examples/test_cond.csn

@@ -1,4 +1,23 @@
 (
+  ; test else
+
+  (cmp 0 5
+    (eq? (fault))
+    (else? (ld r0 15))
+    (lt? (fault)) ; This should produce a warning
+  )
+  (cmp 15 r0
+    (ne? (fault "else did not run")))
+
+  (ld r0 0)
+
+  (cmp 0 5
+    (lt? (nop))
+    (else? (fault "fallthrough to else"))
+  )
+
+  ;
+
   (ld r8 0)
 
   (ld r0 1