Fix #4430 - Add support for -o to save the payload to disk

Fix #4430
No point to save if there's no payload
Well, should be -1
Remove references to Redmine in code

See #4400. This should be all of them, except for, of course, the module
that targets Redmine itself.

Note that this also updates the README.md with more current information
as well.
Missed one in CONTRIBUTING.md
Normalize links to metakitty, unleashed, and wiki
Land #4439, rm Redmine references in code
Land #4437, msfvenoms new output switch
Correct Microsoft security bulletin for ppr_flatten_rec
Land #4450, MSB reference fix
Add stager for hidden bind shell payload
AHOST OptAddress moved to the payload
Handler and block_hidden_bind_tcp deleted
New block_api applied
Add bind_hidden_tcp to payload spec
Merge pull request #7 from wvu-r7/pr/3394

Add bind_hidden_tcp to payload spec
Readd block_hidden_bind_tcp.asm

Because stager_hidden_bind_tcp.asm includes it.
Merge pull request #8 from wvu-r7/pr/3394

Readd block_hidden_bind_tcp.asm
Align shellcode in bind_hidden_tcp
Merge pull request #9 from wvu-r7/pr/3394

Align shellcode in bind_hidden_tcp