Create mock DB setup, postgres integration tests

[bobheadxi]

• Added mock DB setup, with func newTestDBConnection() (*DAL, func(), error) that begins transactions and rolls back after each test.

• Bump postgres driver version (current one is more than a year old), update Update() functions accordingly with new WherePK() requirement. Read up on it a bit and there doesn't seem to be any other breaking changes.

• Change data.dal.db type from *pg.DB to orm.DB, an interface shared between pg.Tx and pg.DB for testing purposes.

• Updated README documentation.

make test-integration

Coverage dropped a bit because a new package has been introduced to Coveralls (it doesn't automatically calculate coverage against all packages, only those that have at least one test)

[coveralls]

Coverage decreased (-2.8%) to 40.259% when pulling db7583ca12d98b219736be877921786d3b3cfb5e on test-db into 5b2b077a36d8e45595f3fae2a249e7427845f417 on master.

[bobheadxi]

rebased