TST: Parameterise tests where needed

[Kai-Striega]

Proposed new feature or change:

Currently NumPy-Financial has many repeating tests for example in tests.test_financial.TestMirr.test_mirr We have the following code that could be parameterised across inputs/data types

    def test_mirr(self):
        val = [-4500, -800, 800, 800, 600, 600, 800, 800, 700, 3000]
        assert_almost_equal(npf.mirr(val, 0.08, 0.055), 0.0666, 4)

        val = [-120000, 39000, 30000, 21000, 37000, 46000]
        assert_almost_equal(npf.mirr(val, 0.10, 0.12), 0.126094, 6)

        val = [100, 200, -50, 300, -200]
        assert_almost_equal(npf.mirr(val, 0.05, 0.06), 0.3428, 4)

        val = [39000, 30000, 21000, 37000, 46000]
        assert_(numpy.isnan(npf.mirr(val, 0.10, 0.12)))

    def test_mirr_decimal(self):
        val = [Decimal('-4500'), Decimal('-800'), Decimal('800'),
               Decimal('800'), Decimal('600'), Decimal('600'), Decimal('800'),
               Decimal('800'), Decimal('700'), Decimal('3000')]
        assert_equal(npf.mirr(val, Decimal('0.08'), Decimal('0.055')),
                     Decimal('0.066597175031553548874239618'))

        val = [Decimal('-120000'), Decimal('39000'), Decimal('30000'),
               Decimal('21000'), Decimal('37000'), Decimal('46000')]
        assert_equal(npf.mirr(val, Decimal('0.10'), Decimal('0.12')),
                     Decimal('0.126094130365905145828421880'))

        val = [Decimal('100'), Decimal('200'), Decimal('-50'),
               Decimal('300'), Decimal('-200')]
        assert_equal(npf.mirr(val, Decimal('0.05'), Decimal('0.06')),
                     Decimal('0.342823387842176663647819868'))

        val = [Decimal('39000'), Decimal('30000'), Decimal('21000'),
               Decimal('37000'), Decimal('46000')]
        assert_(numpy.isnan(npf.mirr(val, Decimal('0.10'), Decimal('0.12'))))