Update returns.md

Fix spelling mistake
Annotation class can't have body
Merge remote-tracking branch 'upstream/master'
Replace textual reference with link.
Merge pull request #107 from jotomo/patch-1

Replace textual reference with link.
Update java-interop.md
Merge pull request #109 from dmitrysobolev/patch-1

Update java-interop.md
Merge pull request #106 from Dacainiao/patch-1

Update returns.md
Update code examples

- delete space before ':' in property/parameter/function type
- add space before ':' in supertypes
- delete empty '()' in class declaration
- other minor stuff like semicolons at EOL, missing spaces, etc.
- fix indent to be the same in each file (should ideally be the same globally)
- change syntax of some Java code to "``` java"
- fix some examples which weren't compilable
Update markup of keywords

A keyword "foo":
*foo*{: .keyword }
Update inline code markup

Use backticks for inline code
Update Ranges and Type-Safe Builders

Add inline code, keyword emphasis and other minor stuff
Unify style of links to Effective Java
Fix asterisk emphasis in several places

Do not emphasize other language names, because they are not emphasized in the
majority of the docs.

Also emphasize object expression/declaration difference
Fix some hyperlinks

Update captions, add some links, remove obsolete ones
Fix typos and improve markup
Merge remote-tracking branch 'upstream/master'