use the correct Namespace class in Model module
use Bundler.setup and explicitly require as needed
reset config to default to rdf_backed
refactored storage api; improve redland impl

storage api now contain just:
- triples(subject, predicate, object, options = {})

introduced TripleIterator for more efficient and convenient iteration of
librdf streams

before/after tests done and saw a 4x speed improvement:

- before
  --Namespace--
  total     0.360000   0.020000   0.380000 (  0.389892)
  avg       0.018000   0.001000   0.019000 (  0.019495)
  --All Namespaces--
  total     4.930000   0.340000   5.270000 (  5.334051)
  avg       0.246500   0.017000   0.263500 (  0.266703)
  --Single Value Equivalents--
  total    10.840000   0.730000  11.570000 ( 11.591968)
  avg       0.542000   0.036500   0.578500 (  0.579598)
  --Single Namespace Value Orthologs--
  total    27.050000   1.780000  28.830000 ( 28.865497)
  avg       1.352500   0.089000   1.441500 (  1.443275)
  --Namespace Value--
  total     2.110000   0.140000   2.250000 (  2.212996)
  avg       0.105500   0.007000   0.112500 (  0.110650)

- after
--Namespace--
total     0.100000   0.000000   0.100000 (  0.109285)
avg       0.005000   0.000000   0.005000 (  0.005464)
--All Namespaces--
total     1.410000   0.040000   1.450000 (  1.459878)
avg       0.070500   0.002000   0.072500 (  0.072994)
--Single Value Equivalents--
total     3.090000   0.110000   3.200000 (  3.214327)
avg       0.154500   0.005500   0.160000 (  0.160716)
--Single Namespace Value Orthologs--
total     7.650000   0.230000   7.880000 (  7.920393)
avg       0.382500   0.011500   0.394000 (  0.396020)
--Namespace Value--
total     0.610000   0.020000   0.630000 (  0.613471)
avg       0.030500   0.001000   0.031500 (  0.030674)