Add CODEOWNERS to auto-assign PRs

Extracted from first commit for each directory. Should be a reasonably good proxy.

CODEOWNERS

+adversarial_crypto/* @dave-andersen
+adversarial_text/* @rsepassi
+attention_ocr/* @alexgorban
+autoencoders/* @snurkabill
+cognitive_mapping_and_planning/* @s-gupta
+compression/* @nmjohn
+differential_privacy/* @panyx0718
+domain_adaptation/* @bousmalis
+im2txt/* @cshallue
+inception/* @shlens @vincentvanhoucke
+learning_to_remember_rare_events/* @lukaszkaiser @ofirnachum
+lfads/* @jazcollins @susillo
+lm_1b/* @oriolvinyals @panyx0718
+namignizer/* @knathanieltucker
+neural_gpu/* @lukaszkaiser
+neural_programmer/* @arvind2505
+next_frame_prediction/* @panyx0718
+object_detection/* @jch1 @tombstone @derekjchow @jesu9 @dreamdragon
+pcl_rl/* @ofirnachum
+real_nvp/* @laurent-dinh
+resnet/* @panyx0718
+skip_thoughts/* @cshallue
+slim/* @sguada @nathansilberman
+street/* @theraysmith
+swivel/* @waterson
+syntaxnet/* @calberti @andorardo
+textsum/* @panyx0718 @peterjliu
+transformer/* @daviddao
+tutorials/embedding/*	@zffchen78 @a-dai
+tutorials/image	@sherrym @shlens
+tutorials/rnn @lukaszkaiser @ebrevdo
+video_prediction/* @cbfinn
+