Create CONTRIBUTING.md

A link to this doc will be displayed at the top of the 'new issue' screen. Additions or corrections are welcome.
Corrected internal links.
Polishing zh translation, 'properties' section of Configuration.
Improve the zh-translation, 'settings' part of configuration.
Polishing the java doc.
Improve the zh-doc, 'typeAliases' section of configuration
Improve the zh-doc, 'typeHandlers' section of configuration
Update java-api.xml

remove wrong spaces
Merge pull request #247 from htynkn/patch-1

Update java-api.xml
Merge pull request #246 from wangdx/master

Some zh-docs improving and one javadoc polishing.