1. Simplify implementation of taosHashCondTraverse
2. Complete function header comments for a few more functions

* Testing

Run through the sample mysql:
taos> create database db;
Query OK, 0 of 0 row(s) in database (0.002475s)

taos> use db;
Query OK, 0 of 0 row(s) in database (0.000252s)

taos> create table t (ts timestamp, a int);
Query OK, 0 of 0 row(s) in database (0.003588s)

taos> insert into t values ('2019-07-15 00:00:00', 1);
Query OK, 1 of 1 row(s) in database (0.001268s)

taos> insert into t values ('2019-07-15 01:00:00', 2);
Query OK, 1 of 1 row(s) in database (0.000265s)

taos> select * from t;
           ts            |      a      |
========================================
 2019-07-15 00:00:00.000 |           1 |
 2019-07-15 01:00:00.000 |           2 |
Query OK, 2 row(s) in set (0.000822s)

taos> drop database db;
Query OK, 0 of 0 row(s) in database (0.001711s)

A few cleanups:
1. Move implementation details (macro definition, SHashEntry and SHashObj
   definition) to hash.c. Only leave relevant APIs in hash.h.
2. Complete function header comments.
3. Correct variable naming from "newSize" to "newCapacity".

A few cleanups:
1. Rename hash node "count" to "refCount" for ease of reading
2. Trailing white space removal of hash.h

* [TS-498]<test>: add a test case for HttpClientPoolUtil

* [TS-498]<fix>: fixed 'no sql input' bug

* throw exception when httpEntity is null

* [TS-498]<fix>: alter Keep Alive Time in RESTful pool
Co-authored-by: Nxywang <xywang@taosdata.com>

* [TS-498]<test>: add a test case for HttpClientPoolUtil

* [TS-498]<fix>: fixed 'no sql input' bug

* throw exception when httpEntity is null

* [TS-498]<fix>: change taosd keepAlive to 30s
Co-authored-by: Nxywang <xywang@taosdata.com>

specify child table name instead using ID in tag field.

add tsClientMerge option to enable or disable client merge row and fix server duplicate row merge bug in skiplist

to binary/nchar through smlDefaultJSONStrType param

[TD-6264]<hotfix>:backport _block_dist() from 2.1 to 2.0 to fix core dump due to tbuf length limitation