Differences in defaults between TiDB and MySQL 5.7

[morgo]

Is it possible to create a manual page (or alternatively append to this manual page) differences in defaults between TiDB and MySQL? My short list:

• TiDB defaults to utf8 (MySQL 5.7 is latin1 - this changes in 8.0 to utf8).
• TiDB defaults and only supports lower_case_table_names=2.
• TiDB's default collation is binary.

[lilin90]

Related content is added to docs in this PR: #591