Bump JavaWriter to 2.4.0.

JavaWriter now handles indentation of multi-line field initializers itself.
Merge pull request #85 from daj/master

Readme update to help newbies
Merge pull request #84 from square/jw/two-four-oh

Bump JavaWriter to 2.4.0.
Add Additional statements for exporting individual Enum Values See #74
Modified the way how generated Enums look like, dropped annotation.
Switch to an indexed for loop for Enum Generation.
Update pom.xml to target javawriter 2.4.0
Use beginConstructor and endConstructor functions instead of method calls + Formatting issues.
Change some test files
Remove warning about var-args being ambigous for null type during method invoke
Remove ProtoEnum annotation from AllTypes.java
Update Reference Test Output Files for removal of ProtoEnum
Clean up imports from code generation and EnumAdapter
Clean up comments and finally ProtoEnum.java from the repository.
Convert to interface ProtoEnum.
Modify test files add implements ProtoEnum clause
fix comment style.
Clean up unused imports.
Fix Checkstyle issues.
Fix up ProtoEnum test output files for import issues. [All Tests passing]
Add Override in code generated files
Fix Comments and missing overrides in test.
Fix up comments
Merge pull request #81 from garena/master

Add Additional statements for exporting individual Enum Values See #74
Remove unnecessary use of map of enum to tag.

Since enums now have direct access to their tag via `getValue()`, alter the generic bounds to facilitate direct access.
Merge pull request #86 from square/jw/sparse-enums

Remove unnecessary use of map of enum to tag.
Add basic Proguard rules to README

I was tempted to suggest that more clever Proguard rules might be possible, e.g. by keeping members with Wire annotations, unfortunately I don't have time to investigate further.

-keepclassmembers class ** {
    @com.squareup.wire.ProtoField public *;
    @com.squareup.wire.ProtoEnum public *;
}