bigtable/bttest: Implement how row filters are implemented.
bigtable/bttest: Implement how row filters are implemented.

Filters are now applied in a simpler, though less efficient manner,
and correctly support nested filters, such as a LatestNFilter inside
a ChainFilters list. This should also make it easier to implement
value transformers.

Fixes #165.

Change-Id: Ic09830604c5d96ac97e4e8469de3f23ffda84c01

hsinhoyeh/gcloud-golang,googleapis/google-cloud-go,Maksadbek/gcloud-golang,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,hsinhoyeh/gcloud-golang,Maksadbek/gcloud-golang,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,googleapis/google-cloud-go