Rephrasing and spelling

Rephrased sentences, some stylistic changes.

Stylistics, grammar and changed string "topic" to "topicname" in one Java example code snippet since topic is a keyword in TDengine.

ci: add 2.6 branch to ci

[TS-1568]

Stylistic changes.

rephrased slightly

Spelling, grammar and stylistic.

Stylistic and grammar changes.

Rephrased sentences.

Rephrasing in some places.

docs: refine a  statement

Minor stylistic changes.

Additions, rephrasing.

Some additions, stylistic changes, grammar, spelling changes.

Added some phrases.
Stylistic changes.

docs: port the changes by chait from 2.4 to 2.6 in functions.md

stylistic change

grammatical, stylistic and one spelling change.

Minor changes - grammatical, stylistic