CLI: improve diagnostic message format

- render the whole line where the error/warning points to, if any, and another
  line with '^', like other compilers do
- lowercase diagnostic severity
- decapitalize the message if it doesn't start with a proper name

compiler/testData/repl/analyzeErrors.repl

@@ -1,5 +1,7 @@
 >>> fun foo() = 765
 >>> foo(1)
-ERROR: /line2.kts: (1, 5) Too many arguments for internal final fun foo(): kotlin.Int defined in <script>
+/line2.kts:1:5: error: too many arguments for internal final fun foo(): kotlin.Int defined in <script>
+foo(1)
+    ^
 >>> foo()
 765