Add AO_index (#55)

input_data/AO_index/meta.yaml

+repo_name: AO_index
+
+people:  Willi Rath (<wrath@geomar.de>)
+
+http_path_remote: https://git.geomar.de/data/AO_index
+
+git_path_remote: git@git.geomar.de:data/AO_index
+
+repo_description: |
+    Arctic Oscillation time series from
+    <http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml>.
+
+prefixes: data doc
+
+data:
+
+    - url: "http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii"
+      prefix: data
+      file_name: monthly.ao.index.b50.current.ascii
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+doc:
+
+    - url: "http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml"
+      file_name: www.cpc.ncep.noaa.gov_products_precip_CWlink_daily_ao_index_ao.shtml
+      prefix: doc
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+    - url: "http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442%282000%29013%3C3994%3ADFITSP%3E2.0.CO%3B2"
+      file_name: Higgins_et_al_2000.pdf
+      prefix: doc
+      method: !!python/name:data_repo_renderer.CurlSingleFile
+
+    - url: "http://onlinelibrary.wiley.com/doi/10.1029/2001GL013660/pdf"
+      file_name: www.cpc.ncep.noaa.gov_products_precip_CWlink_daily_ao_index_ao.shtml
+      prefix: Zhou_et_al_2001.pdf
+      method: !!python/name:data_repo_renderer.CurlSingleFile