Improve KlibSignatureVersion.toString format for LATEST version (#220)

Closes #219

Author: fzhinkin

src/main/kotlin/api/klib/KlibSignatureVersion.kt

@@ -30,6 +30,10 @@ public class KlibSignatureVersion internal constructor(internal val version: Int
     }
 
     override fun toString(): String {
-        return "KlibSignatureVersion($version)"
+        val versionStr = when(version) {
+            LATEST.version -> "LATEST"
+            else -> version.toString()
+        }
+        return "KlibSignatureVersion($versionStr)"
     }
 }

src/test/kotlin/tests/KlibSignatureVersionTest.kt

@@ -36,4 +36,10 @@ class KlibSignatureVersionTest {
         assertEquals(KlibSignatureVersion.of(1).hashCode(), KlibSignatureVersion.of(1).hashCode())
         assertNotEquals(KlibSignatureVersion.of(1).hashCode(), KlibSignatureVersion.of(2).hashCode())
     }
+
+    @Test
+    fun toStringFormat() {
+        assertEquals("KlibSignatureVersion(LATEST)", KlibSignatureVersion.LATEST.toString())
+        assertEquals("KlibSignatureVersion(42)", KlibSignatureVersion.of(42).toString())
+    }
 }