issue #198: rename Header -> HeaderPair to harvest the names for new annotations
fix issue #198: add new @Headers and @Header annotations
issue #198: validate header names per rfc 2616
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")
Merge remote-tracking branch 'ac/header-params' into jw/rewrite-all-the-things

Conflicts:
	retrofit/src/main/java/retrofit/http/RequestBuilder.java
	retrofit/src/main/java/retrofit/http/RequestHeaders.java
	retrofit/src/main/java/retrofit/http/RestAdapter.java
	retrofit/src/main/java/retrofit/http/RestMethodInfo.java
	retrofit/src/main/java/retrofit/http/client/ApacheClient.java
	retrofit/src/main/java/retrofit/http/client/Header.java
	retrofit/src/main/java/retrofit/http/client/Request.java
	retrofit/src/main/java/retrofit/http/client/Response.java
	retrofit/src/main/java/retrofit/http/client/UrlConnectionClient.java
	retrofit/src/test/java/retrofit/http/RequestBuilderTest.java
	retrofit/src/test/java/retrofit/http/client/ApacheClientTest.java
	retrofit/src/test/java/retrofit/http/client/UrlConnectionClientTest.java
Review feedback.
Merge pull request #202 from square/jw/rewrite-all-the-things

Rewrite annotations to be more descriptive.