Revise functions in PathReadWrite

- Adjust implementations to avoid excessive vararg copies
- Remove options from forEachLine, it doesn't make much sense and
isn't consistent with the other read* functions.
- Revise inlineness of functions in PathReadWrite
- Compact implementations of those that are remained inline.
- Clarify docs of functions for reading the entire file

#KT-19192

libraries/stdlib/jdk7/test/PathReadWriteTest.kt

@@ -35,7 +35,7 @@ class PathReadWriteTest {
         writer.close()
 
         val list = ArrayList<String>()
-        file.forEachLine(charset = Charsets.UTF_8, options = arrayOf(StandardOpenOption.READ)) {
+        file.forEachLine(charset = Charsets.UTF_8) {
             list.add(it)
         }
         assertEquals(listOf("Hello", "World"), list)