Add support for accessing nested items in BoxList using numpy-style tuple indexing.

[Bit0r]

Allow BoxList to use numpy-style tuple indexing, similar to l[0,1,2,3], which is equivalent to l[0][1][2][3].

[Bit0r]

@cdgriffith Could you approve the workflow review, please?

[cdgriffith]

This would need a new feature flag if added. As tuples are supported dictionary characters themselves.

Consider:

from box import Box
bx = Box({0: {1: {2: {3: 3}}}, (0, 1, 2, 3): 4})
print(bx[0,1,2,3])
# 4 

[Bit0r]

I have implemented this feature only in the BoxList class, whereas Box is a different class and will still output normally. Using the following code in the unit tests is not a problem:

bx = Box({0: {1: {2: {3: 3}}}, (0, 1, 2, 3): 4})
assert bx[0, 1, 2, 3] == 4

But I will add some error messages to make it more user-friendly.

[Bit0r]

My code only works for list and its subclasses. The first layer must be BoxList, and dict and its subclasses cannot appear in the middle.

[Bit0r]

@cdgriffith Do you think there are any other problems with the code?

[Bit0r]

I don't know how to program with PyPy, and I can't provide an equivalent version of it.

[cdgriffith]

Sorry for delay, I like the addition!

The pypy things is failing even on master as of now, need to sort that out so no something with this code.