Reworked the tests, read more

I've brought the tests up to scratch, except for compounds im the
parser, because I'm too damn tired to do that over SSH. It looks like
collections are right-recursive, whixh was unintended but still works
just fine.

I've also added the '--verbose' flag to the repl to control the
debugging output.

Several obscure bugs have been fixed, and comments have been tweaked.

Mustfail tests are still needed, but that's a low priority. See #142.

Fixed #151

tests/integrations/test_keyword_print.toy

@@ -0,0 +1,21 @@
+//basic print statement
+print 42;
+
+//print complex expressions
+print 3 * 5;
+
+//print a string
+print "Hello world!";
+
+//print a concatenated string
+print "Hello" .. "world!";
+
+//print with escaped characters
+print "\tHello\nworld";
+
+//print from a substring string
+print "Hello world"[0,5];
+
+//print from a substring, after a concat
+print ("hello" .. "world")[2,6];
+