Add binary conversion calls and rspec tests

[bwatters-r7]

Added binary calls and rpsec tests.
To anyone testing: I hit a couple bugs in the single payloads, but I'm going to PR that to master next. There's a small bug in the sign extension for the LPORT and there's an minor implementation detail in argument passing that busybox does not like.

[bwatters-r7]

Payload fixes: rapid7#21519

[bwatters-r7]

I have some suspicions this is unrelated:

rspec ./spec/modules/payloads_spec.rb[1:326:1:1:3] # modules/payloads php/meterpreter_reverse_tcp it should behave like payload cached size is consistent php/meterpreter_reverse_tcp has a valid cached_size

Not sure what I did that could have changed the cache size of php meterpreter?
I'm hoping that merging this and rebasing will make everything happy.

[bcoles]

Not sure what I did that could have changed the cache size of php meterpreter?

It is likely unrelated. This was an ongoing issue at the time of my PR to the Metasploit master branch. I haven't rebased since.