doc: updated the copyright years.

style: fixed coding style issues caught by ngx-releng.

doc: we now work with nginx cores as new as 1.13.6.

doc: we now work with many more nginx versions as far as 1.9.3.

Merge branch 'master' of github.com:openresty/rds-csv-nginx-module

minor coding style fixes.

updated docs to reflect recent changes.

bugfix: the output buffer size would get wrong when the affected_rows…

… field is larger than a single-digit number. thanks Wendal Chen for reporting this by using clang.

bugfix: fixed a compilation error when DDEBUG=1. thanks 郭颖.

updated .gitignore.