re-structure Java API, add Scala API and consolidate the names of Java/Scala API

jvm-packages/README.md

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+# xgboost4j
+this is a java wrapper for xgboost 
+
+the structure of this wrapper is almost the same as the official python wrapper.
+
+core of this wrapper is two classes:
+
+* DMatrix: for handling data
+
+* Booster: for train and predict
+
+## usage:
+  please refer to [xgboost4j.md](doc/xgboost4j.md) for more information.
+
+  besides, simple examples could be found in [xgboost4j-demo](xgboost4j-demo/README.md)
+ 
+
+## build native library
+
+for windows: open the xgboost.sln in "../windows" folder, you will found the xgboost4j project, you should do the following steps to build wrapper library:
+ * Select x64/win32 and Release in build
+ * (if you have setted `JAVA_HOME` properly in windows environment variables, escape this step) right click on xgboost4j project -> choose "Properties" -> click on "C/C++" in the window -> change the "Additional Include Directories" to fit your jdk install path.
+ * rebuild all
+ * double click "create_wrap.bat" to set library to proper place
+
+for linux: 
+ * make sure you have installed jdk and `JAVA_HOME` has been setted properly
+ * run "create_wrap.sh"
+
+for osx:
+ * make sure you have installed jdk
+ * for single thread xgboost, simply run "create_wrap.sh"
+ * for build with openMP, please refer to [build.md](../doc/build.md) to get openmp supported compiler first, and change the line "dis_omp=1" to "dis_omp=0" in "create_wrap.sh", then run "create_wrap.sh"