Add Moondream transformer implementation and example (#1970)

* moondream implementation

* add moondream example

* change config default activation

* Add assets and integrate phi mixformer with example

* Make use of kv cache and fix seq_len bug; Clean up example code

* Add README link to example

* Remove pos_embed scaling; Remove assets; Add to README; Expand VisionConfig

* Delete image

* Use apply instead of forward

candle-transformers/src/models/mod.rs

@@ -24,6 +24,7 @@ pub mod mistral;
 pub mod mixformer;
 pub mod mixtral;
 pub mod mobileone;
+pub mod moondream;
 pub mod mpt;
 pub mod persimmon;
 pub mod phi;