building rl4j for 0.9.2-SNAPSHOT

# building rl4j for the latest snapshot (mvnrepository still doesn't have the latest build)
# build pipeline >> javacpp -> libnd4j -> nd4j -> DataVec -> deeplearning4j -> rl4j
# https://github.com/deeplearning4j/rl4j/issues/73#issuecomment-335732797

0. note about maven version. it must be latest (running 3.5.0)
1. install cmake
   1.1 wget https://cmake.org/files/v3.11/cmake-3.11.0-rc2-Linux-x86_64.sh
   1.2 chmod a+x cmake-3.6.2-Linux-x86_64.sh
   1.3 mkdir /opt/cmake
   1.4 sudo sh cmake-3.11.0-rc2-Linux-x86_64.sh --prefix=/opt/cmake --skip-license
   1.5 ln -s /opt/cmake/bin/cmake /usr/local/bin/cmake
   1.6 cmake --version
2. clone the repos
   2.1 git clone https://github.com/bytedeco/javacpp.git
   2.2 git clone https://github.com/deeplearning4j/libnd4j.git
   2.3 git clone https://github.com/deeplearning4j/nd4j.git
   2.4 git clone https://github.com/deeplearning4j/DataVec.git
   2.5 git clone https://github.com/deeplearning4j/deeplearning4j.git
   2.6 git clone https://github.com/deeplearning4j/rl4j.git
3. export LIBND4J_HOME=/home/user/directory/libnd4j  # this is the path of the libnd4j in bashscript
4. build the repos serially (no cuda)
   4.1 cd javacpp, mvn clean install -DskipTests
   4.2 cd libnd4j, mvn clean install -DskipTests
   4.3 cd nd4j, mvn clean install -DskipTests -pl '!nd4j-backends/nd4j-backend-impls/nd4j-cuda,!nd4j-backends/nd4j-backend-impls/nd4j-cuda-platform'
   4.4 cd DataVec, mvn clean install -DskipTests
   4.5 cd deeplearning4j, mvn clean install -DskipTests -pl '!./deeplearning4j-cuda/'
   4.6 cd rl4j, mvn clean install -DskipTests