Improve zh-doc, 'Handling Enums' section of configuration.
Improve zh-doc, 'objectFactory' and 'plugins' section of configuration.
Polishing the en-doc, remove the duplicated word.
Improve zh-doc, 'environments','databaseIdProvider' and 'mappers' sections of configuration.
Merge pull request #251 from wangdx/master

Improve the rest of configuration doc and one duplicated word in en doc.