Read packed fields for protobuf compability

Protobuf allows some fields to be encoded packed:

https://developers.google.com/protocol-buffers/docs/encoding#optional

This patch will allow protostuff to read these fields.
Fix curly formatting
Update after code review
Update CodedInput with packed support
Remove wildcard import in CodedInput
Simplify readFieldNumber
Merge branch 'master' into mzeo/allow-packed-repeated

Conflicts:
	protostuff-core/src/main/java/io/protostuff/CodedInput.java
Merge pull request #44 from mzeo/allow-packed-fields

Add support for packed fields.