Minimalist doc for HashField (cf #55)
Merge branch 'master' into fields-corrections

Conflicts:
	doc/fields.rst
Merge pull request #73 from twidi/fields-corrections

Fields corrections
Rename the "get_new" method of pk-fields to "_validate"
RedisModel: Make self.pk.get() do the work previously done by self.get_pk()
Get rid of get_pk

(using _pk in tests)
Raise DoesNotExist instead of ValueError if object not found
Merge pull request #75 from twidi/work-on-pk

Get rid of get_pk, and raise DoesNotExist when needed, instead of ValueError