* docs: python document part2

* docs: refine some words

* docs: typo

* docs: add R example source code

* test: check if RJDBC was installed

* test: add R test scripts

* test: chmod of test_R.sh

* test: fix test_go.sh; add R sample to document

* test: add test scripts to cases.task

* test: fix errors caused by  tset_python.sh and test_java.sh

* test: fix  test_python.sh

* test: modify java test case and improve opentsdb-json.mdx

* test: fix test_R.sh

* add c examples and subscribe examples files for other languages

* add query example

* c sample code

* c query example

* doc fix

* rust sql insert example

* rust schemaless examples

* rust stmt examples

* rust query example

* remove go async

* format code

* go sql insert example

* fix go doc bug

* adjust cluster part; change mysql to sql

* add go connect example using af

* go stmt example

* go influxdb line example

* go telnet line insert example

* reduce sample data

* go json insert example

* go query example

* code review

* python insert example

* python stmt example

* python query example

* python async exmaple

* python json example

* java json example

* add sample code

* add sample code

* add example

* add connect examples