Add annotation-based method(s) for injecting properties during serialization

[cowtowncoder]

(note: replaces #322)

A very common need that is not currently supported is the ability to insert additional properties in JSON (etc) output, without requiring physical POJO properties. This could include things like:

1. Injecting Jackson attribute (2.4) values (from Add support for annotation-based integration with attributes (see #319) #322)
2. Injecting custom BeanPropertyWriter instances (or perhaps a new sub-type), giving more control

Now; although there are some existing annotations that could work her (@JsonSerialize, specifically, from databidn package), it might make sense to add a new annotation or annotations.

Some things to consider:

1. How to specify ordering of these attributes? While @JsonPropertyOrder needs to take these into account, it'd make sense to at least specify "default" placement before or after "regular" properties.
2. For attributes, should name of attribute be 1-to-1 with property name to use? (fine as default, but if/how to allow override?)
3. How to minimize amount of annotation decorations to use, without exploding number of annotations; esp. considering need to support (1) and ()