[SPARK-2923][MLLIB] Implement some basic BLAS routines

Having some basic BLAS operations implemented in MLlib can help simplify the current implementation and improve some performance.

Tested on my local machine:

~~~
bin/spark-submit --class org.apache.spark.examples.mllib.BinaryClassification \
examples/target/scala-*/spark-examples-*.jar --algorithm LR --regType L2 \
--regParam 1.0 --numIterations 1000 ~/share/data/rcv1.binary/rcv1_train.binary
~~~

1. before: ~1m
2. after: ~30s

CC: jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #1849 from mengxr/ml-blas and squashes the following commits:

ba583a2 [Xiangrui Meng] exclude Vector.copy
a4d7d2f [Xiangrui Meng] Merge branch 'master' into ml-blas
6edeab9 [Xiangrui Meng] address comments
940bdeb [Xiangrui Meng] rename MLlibBLAS to BLAS
c2a38bc [Xiangrui Meng] enhance dot tests
4cfaac4 [Xiangrui Meng] add apache header
48d01d2 [Xiangrui Meng] add tests for zeros and copy
3b882b1 [Xiangrui Meng] use blas.scal in gradient
735eb23 [Xiangrui Meng] remove d from BLAS routines
d2d7d3c [Xiangrui Meng] update gradient and lbfgs
7f78186 [Xiangrui Meng] add zeros to Vectors; add dscal and dcopy to BLAS
14e6645 [Xiangrui Meng] add ddot
cbb8273 [Xiangrui Meng] add daxpy test
07db0bb [Xiangrui Meng] Merge branch 'master' into ml-blas
e8c326d [Xiangrui Meng] axpy

(cherry picked from commit 9038d94e1e50e05de00fd51af4fd7b9280481cdc)
Signed-off-by: Xiangrui Meng <meng@databricks.com>
[MLlib] Correctly set vectorSize and alpha

mengxr
Correctly set vectorSize and alpha in Word2Vec training.

Author: Liquan Pei <liquanpei@gmail.com>

Closes #1900 from Ishiihara/Word2Vec-bugfix and squashes the following commits:

85f64f2 [Liquan Pei] correctly set vectorSize and alpha

(cherry picked from commit f0060b75ff67ab60babf54149a6860edc53cb6e9)
Signed-off-by: Xiangrui Meng <meng@databricks.com>