* update how to compile the site
* upgrade version to v0.12
* remove download links of legacy versions, add -c parameter for cli in doc

[IOTDB-761]cherry-picked from v0.10: flink-tsfile-connecto and flink-example dependency conflict: "Some Enforcer rules have failed. Look above for specific messages explaining why the rule failed" (#1365)

* fix Dependency convergence error in flink-tsfile-connector

* [IOTDB-503] Add checkTimeseriesExists for session

* [IOTDB-565] MQTT Protocol Support

* [IOTDB-565] upgrade fastjson to latest version

* update rocketmq-example with session API

* reduce project version declaration (which can make releasing easily)

o	I moved the static parts of the client and server distributions to “src/assembly/resources” and added an assembly that builds the client and server inside the target directory (You need to update the documentation on this)
o	The sever is now available at server/target/iotdb-server-0.9.0-SNAPSHOT
o	The client is now available at client/target/iotdb-client-0.9.0-SNAPSHOT
o	I updated the integration tests to work with these new locations
-	I updated the distribution module (binary-distribution) to simply include and unpack the client and server assemblies, which greatly simplifies the assembly itself.
-	In the integration-tests you use a process builder to get the current working directory … you can access this in the “user.dir” System property.
-	There was a large mixture of artifacts with different versions in the classpath.
o	I set all versions to the same using a big dependencyManagement block in the master pom
o	I removed the version of every external dependency and moved it into the main dependencyManagement block in the root pom (except dependencies only used in the examples, for these I added a dependencyManagement block in the example pom). This way you instantly identify external dependencies.
o	I added an enforcer rule to fail the build if two differing versions of one artifact are being used in the build (This should eliminate this problem from re-occuring)
o	I replaced the usage of “${project.version}” with the real version (There is no need to manually update these versions and this way when looking at the pom you instantly know the version … keep in mind if an artifact is deployed to maven central, the user doesn’t have the code and therefore he always has to scroll up to the top in order to see which version is used)
-	There were some imports related to Jdk 11 no longer providing some APIs, I moved those imports to a maven profile, which is activated based on the JDK version
-	HDFSInputTest created a file in “spark/test/” … if the test failed, the rat plugin would complain the next time it’s run.

I checked the build with all tests on Oracle-Java 8, Open-JDK 11, Oracle-JDK 12.

Added sha512 code for binary package.
Changed version to 0.8.0-SNAPSHOT.

* upgrade mvn wrapper version from 3.5.0 to 3.6.0

* replace org.json by alibaba.fastjson

* remove LGPL 2.1 license of logback

* update license and NOTICE

* add CDDL and EDL license

* add demo of kafka

* add demo of rocketmq

* add readme of example project

* fix a mistake in IoTDBConnectionParams in jdbc module

* add examples as a module

1. modify asf header for each file; 2. enable apache-rat-plugin; 3. add more exclusive files on apache-rat-plugin and license-maven-plugin, i.e., *.json, *.md, and *.csv

* format Almost for obeying Google Java Style.

* fix the problem of checkstyle

* fix license-format template file location

* add apache header check plugin

* add fotmat plugin

* move format code to verify phase

* change to compile phase

* change to verify phase

* remove special char in .travis

* remove useless code

* add apach header and format codes

* Update MavenWrapperDownloader.java