Mathjs: Support +=

[toddmedema]

Example:
a = 1
a += 1 should set a = 2 and return 2

[josdejong]

Thanks for the suggestion, I miss this operator too every now and then.

[Nekomajin42]

Will it work with -=, *= and /= too?

[josdejong]

Yes we we should add all of them :)

[Nekomajin42]

Not strictly related, but what about the ES7 exponential operator (**)?

[josdejong]

Well, we already have ^ for exponentiation, adding ** too would not really help I think.

[harrysarson]

Let's discuss in #1134.