Merge pull request #321 from aparo/develop

Release 0.20.1
No reason to forbid empty values()

Django queryset.values() does not force it and pyes code as well.
IdsQuery: check for list instance, not basestring

Ids may be strings, ints, whatever. Better to check if 'values' parameter
is a list, if not, wrap the value into a single-element list.
Fix typo
Merge pull request #326 from freelancer37/patch-1

Fix typo
Added missing import in managers.py.
Merge pull request #327 from abelldh/fix-mapping-import

Added missing import in managers.py.
fix DateHistogramFacet reference from 'zone' to 'time_zone' and add additional params
Merge pull request #329 from stevencdavis/master

fix DateHistogramFacet reference from 'zone' to 'time_zone' and add params
add optional 'headers' param to allow for {'Accept-Encoding': 'gzip, deflate'} and other custom headers
Merge pull request #330 from stevencdavis/master

add optional 'headers' param to allow for 'Accept-Encoding' headers
Added InvalidIndexNameException
Merge pull request #333 from jake92m/master

Added InvalidIndexNameException
Merge pull request #322 from mindflayer/patch-2

No reason to forbid empty values()
Merge pull request #325 from CGenie/cgenie

IdsQuery: check for list instance, not basestring
Merge branch 'master' of https://github.com/aparo/pyes into feature/cleanup_deprecation