Rename "coordinates" to "indices"?

[shoyer]

For users of pandas, the xray interface would be more obvious if we referred to what we currently call "coordinates" as "indices."

This would entail renaming the coordinates property to indices, xray.Coordinate to xray.Index and the xray.Coordinate.as_index property to as_pandas_index (all with deprecation warnings).

Possible downsides:

1. The xray data model would be less obvious to people familiar with the NetCDF.
2. There is some potential for confusion between xray.Index and pandas.Index:
   • The only real difference is that xray's Index is a xray.Variable object, and thus is dimension aware and has attributes.
   • In principle, xray.Index should have all the necessary properties to act like an index (or rather, it already has most of these properties and should get the rest).
   • Unfortunately, pandas doesn't accept non-pandas.Index objects as indices, nor will it properly convert an xray.Index into a pandas.Index.

[shoyer]

Here is a (partial) fix for the pandas issue: pandas-dev/pandas#7270

[shoyer]

Some research was revealed that both "indices" and "indexes" are valid plural forms for "index": http://english.stackexchange.com/questions/61080/indexes-or-indices

I am inclined to go ahead with this change but will need to decide on if we should use "indexes" or "indices" first.

My inclination is to go for "indexes" since it seems to be more popular in this context: http://www.googlefight.com/index.php?lang=en_GB&word1=%22database+indices%22&word2=%22database+indexes%22