Rewrite annotations to be more descriptive.

Method level:
 * `@FormEncoded`
 * `@Multipart`

Parameter level:
 * `@Path` - URL path replacement
 * `@Query` - URL query string
 * `@Pair` - Form-encoding pair
 * `@Part` - Multi-part part
 * `@Body` - Single-object body (Old `@SingleEntity`)

This removes support for `@QueryParam`/`@QueryParams` in favor of including constants in the declared URL itself. e.g.,

    @GET("/list?foo=bar")