* remove jdk version constrain for jdk8 and 11. (now only jdk<1.8u40 is forbidden)

* add apache-rat for .checkstyle file

* update doc

* add metrics service for visualizing query history, query time cost and query plans.  The display time is accurate to milliseconds, contributed by @xijunmu (daihui_iot)

* Refactor TsFile storage on HDFS

* fix bug using "both condition 2 and 3 should respond with error message"

* Revert "fix bug using "both condition 2 and 3 should respond with error message""

This reverts commit 3ae6c176.

* change name of spark package

* add a framework

* add start-up script of LogVisualizer

* add documentations of log visualizer

* Rephrase document
Change group logic of visualizer
Add sum to statistics

* add request of knowing regular expressions in documents
add comment to the example plan

* add pre set plans
increase usablility

* add result export

* add a command line tool

* support selecting multiple log files

* update docs and examples

* fix querying non-existing paths in where clause"

This reverts rename hadoop package , commit 42c62e7e.

* change hadoop package name

*  change magic string and add version in TsFile

* add group by device function
* fix bug IOTDB-244 by making server deduplicate

change hive's copyright from 2019 to 2018 for being consistent with github.com/apache/hive NOTICE file

* Add sql interface in session

* add external sort in time range query

* Add Chinese version for hadoop-connector doc

* Add doc for hadoop connector

* add client-py

* add hadoop-tsfile connector

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

* IOTDB-242 fix mvn integration-test failed because the files in the target folder changes (server and client module)

* fix bug using "both condition 2 and 3 should respond with error message"

Change javdoc to block comment.

* add delete storage group interface in session

* Add interface for showing devices

* Avoid creating a new ChunkGroupFooter object.

Delete timeseries in session