[CODEC-272] Add RandomAccessFile digest methods #31.

- This is a slightly different version from
#31
- Refactor updateDigest(MessageDigest,RandomAccessFile) into an new
private updateDigest(MessageDigest,FileChannel) as possible public
candidate.
- Do NOT seek to 0 on a RandomAccessFile before calling updateDigest():
We do not do this for ByteBuffer input, so do not do it here and be
consistent to assume that when the caller says 'digest this' then do it
from where the input stands (like a stream).
- Add methods in the file to keep methods in alphabetical order.
- Closes #31.

src/test/java/org/apache/commons/codec/digest/MessageDigestAlgorithmsTest.java

@@ -167,7 +167,7 @@ public void testNonBlockingDigestRandomAccessFile() throws IOException {
                         DigestUtils.getDigest(messageDigestAlgorithm), getTestRandomAccessFile()
                 )
         );
-
+        getTestRandomAccessFile().seek(0);
         Assert.assertArrayEquals(expected,
                 DigestUtils.digest(
                         DigestUtils.getDigest(messageDigestAlgorithm), getTestRandomAccessFile()