Keep gadgets when setting registers via setattr/call

[hackedd]

Adding the gadgets to the chain (instead of their address) generates slightly better descriptions when the gadget corresponds to a symbol (and avoids having to go through unresolve).

To take the example from the doctest in __call__:

    >>> context.clear(arch='amd64')
    >>> assembly = 'pop rax; pop rdi; pop rsi; ret; pop rax; ret;'
    >>> e = ELF.from_assembly(assembly)
    >>> r = ROP(e)
    >>> r(rax=0xdead, rdi=0xbeef, rsi=0xcafe)
    >>> print(r.dump())
    0x0000:       0x10000000 pop rax; pop rdi; pop rsi; ret
    0x0008:           0xdead
    0x0010:           0xbeef
    0x0018:           0xcafe

The first item in the chain previously had no description, because there is an unnamed symbol with that address.

[heapcrash]

Cool stuff! Mind updating CHANGELOG.md (in the dev section) and then we can merge this?

Also what is this magic r(rax=0xdead, rdi=0xbeef, rsi=0xcafe) syntax. I don't remember ever seeing that before, but it's really great!

[hackedd]

Is there anything else that needs to be done to merge this?

[heapcrash]

It would be nice if we had describe slots for each value, so we knew which registers were being populated in each slot.

That said, that can be saved for the future.