all: add support for unpickling array.array values

[sbinet]

Fixes #2.

[sbinet]

PTAL @marco-nicola.

For some reason, trying to unpickle the data generated for the L and Q array.array type codes, fails with:

--- FAIL: TestP4Carray (0.00s)
    --- FAIL: TestP4Carray/L (0.00s)
        pickle_test.go:789: unknown opcode: 0x27 '''
        pickle_test.go:751: got=<nil>, want=[0 1 2 3]
    --- FAIL: TestP4Carray/Q (0.00s)
        pickle_test.go:789: unknown opcode: 0x27 '''
        pickle_test.go:751: got=<nil>, want=[0 1 2 3]

also, I couldn't test all the UTF cases (UTF-{16,32} x {LittleE, BigE}).
so, coverage for the u typecode isn't too great.