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/integration/ant/jvm/jvmClasspath/build.log.expected

@@ -3,7 +3,9 @@ Buildfile: [TestData]/build.xml
 
 build:
   [kotlinc] Compiling [[TestData]/hello.kt] => [[Temp]/hello.jar]
-  [kotlinc] WARNING: [TestData]/hello.kt: (15, 9) Variable 'result' is never used
+  [kotlinc] [TestData]/hello.kt:15:9: warning: variable 'result' is never used
+  [kotlinc]     val result = "$a$c$e$f$j"
+  [kotlinc]         ^
      [java] OK
 
 BUILD SUCCESSFUL