Deprecate msfpayload and msfencode

See #4326, but it does not close it.
Email over E-mail

While I believe "e-mail" is the actually correct spelling, we tend to
say "email" everywhere else. See:

````
todb@mazikeen:~/git/rapid7/metasploit-framework$ grep -ri "print.*email"
modules/ | wc -l
19
[ruby-2.1.5@metasploit-framework](fixup-grammar)
todb@mazikeen:~/git/rapid7/metasploit-framework$ grep -ri
"print.*e-mail" modules/ | wc -l
1
````
Margins on description, PowerShell not Powershell
Land #4334, @todb-r7's cosmetic fixes
Fix prompt coloring on Windows

MSP-11669

Set output stream for RbReadline (rl_outstream) to the
Rex::Ui::Text::Output::Stdio, which will use translate the ANSI color
escapes to set_color calls in Windows.
Error messages for the python meterpreter
Remove file exists check from stdapi_fs_delete_file
Land #4329, zeroSteiner's error messages for python meterpreter
Land #4337 - Fix prompt coloring on Windows
Add a link to PR #4333 in the message

That way, people can see why this is if they care to.

While we have a link to the blog post at http://r-7.co/msfvenom-2015 , I
fear that by the time spring of 2015 rolls around, we'll be on a
different blogging platform and the link may be busted. I'm certain
we'll still be on GitHub then, though.
Land #4333 with URL pointer, ty @wchen-r7

Long live msfvenom!

People who have a bug or complaint about msfencode or msfpayload should
be pointed at http://r-7.co/msfvenom-2015

See #4326 (and close it?)