[SPARK-1945][MLLIB] Documentation Improvements for Spark 1.0

Standalone application examples are added to 'mllib-linear-methods.md' file written in Java.
This commit is related to the issue [Add full Java Examples in MLlib docs](https://issues.apache.org/jira/browse/SPARK-1945).
Also I changed the name of the sigmoid function from 'logit' to 'f'. This is because the logit function
is the inverse of sigmoid.

Thanks,
Michael
If we pick the values after join (line 163), this block could be simplified:

~~~
    JavaRDD<Tuple2<Double, Double>> ratesAndPreds =
      JavaPairRDD.fromJavaRDD(ratings.map(
        new Function<Rating, Tuple2<Tuple2<Integer, Integer>, Double>>() {
          public Tuple2<Tuple2<Integer, Integer>, Double> call(Rating r) {
            return new Tuple2<Tuple2<Integer, Integer>, Double>(
              new Tuple2<Integer, Integer>(r.user(), r.product()), r.rating());
          }
        }
      )).join(predictions).values();
    double MSE = JavaDoubleRDD.fromRDD(ratesAndPreds.map(
      new Function<Tuple2<Double, Double>, Object>() {
        public Object call(Tuple2<Double, Double> pair) {
          double err = pair._1() - pair._2();
          return err * err;
        }
      }
    ).rdd()).mean();
~~~