Wrote tests and fixed bugs

  --------------------- ------ ------ ------ ------ ------ ------ -----
  File                    stmt   bran   cond    sub    pod   time total
  --------------------- ------ ------ ------ ------ ------ ------ -----
  Mandel.pm               86.2   56.2    n/a   92.9  100.0   56.3  83.0
  Mandel/Collection.pm    70.6   45.0  100.0   63.2  100.0    1.7  67.8
  Mandel/Document.pm      97.0   79.5   66.7   95.5  100.0   40.8  91.7
  Mandel/Model.pm         96.0   71.4    n/a   90.0   66.7    1.1  89.6
  Mandel/Relationship.pm  60.0    0.0    n/a   66.7    n/a    0.1  53.3
  Relationship/HasMany.pm 69.0    0.0   50.0   75.0  100.0    0.1  63.5
  Relationship/HasOne.pm  41.2    0.0    n/a   62.5  100.0    0.0  37.7
  --------------------- ------ ------ ------ ------ ------ ------ -----
  Total                   80.8   56.2   70.0   80.7   96.3  100.0  76.7
  --------------------- ------ ------ ------ ------ ------ ------ -----

  All tests successful. Files=11, Tests=97. Result: PASS