Added error handling to msfvenom when generating payloads

### Added error handling to msfvenom when generating payloads
*Ugly error messages*

    root@kali ~/metasploit-framework$ ./msfvenom -p windows/meterpreter/reverse_tcp                                                                                                          1 ↵ master
    /root/metasploit-framework/lib/msf/core/module.rb:620:in `validate': The following options failed to validate: LHOST. (Msf::OptionValidateError)
         from /root/metasploit-framework/lib/msf/core/encoded_payload.rb:65:in `generate'
         from /root/metasploit-framework/lib/msf/core/encoded_payload.rb:25:in `create'
         from /root/metasploit-framework/lib/msf/base/simple/payload.rb:53:in `generate_simple'
         from /root/metasploit-framework/lib/msf/base/simple/payload.rb:137:in `generate_simple'
         from ./msfvenom:343:in `<main>'

    root@kali ~/metasploit-framework$   


### Fixed msfvenom when displaying options
*Doesn't display information regarding command line arguments*

    root@kali ~/metasploit-framework$ ./msfvenom -p windows/meterpreter/reverse_tcp LHOST=127.0.0.1 LPORT=4321 -o                                                                                                        ✹master
    [*] Options for payload/windows/meterpreter/reverse_tcp
    
        Name      Current Setting  Required  Description
        ----      ---------------  --------  -----------
        EXITFUNC  process          yes       Exit technique: seh, thread, process, none
        LHOST                      yes       The listen address
        LPORT     4444             yes       The listen port
    root@kali ~/metasploit-framework$               


### Altered msfvenom options to match msfpayload summary
*Wasn't displaying as much information*

    root@kali ~/metasploit-framework$ ./msfvenom -p windows/meterpreter/reverse_tcp LHOST=127.0.0.1 LPORT=4321 -o                                                                             ✹master
    
           Name: Windows Meterpreter (Reflective Injection), Reverse TCP Stager
         Module: payload/windows/meterpreter/reverse_tcp
        Version: $Revision$
       Platform: Windows
           Arch: x86
    Needs Admin: No
     Total size: 290
           Rank: Normal
    
    Provided by:
      skape <mmiller@hick.org>
      sf <stephen_fewer@harmonysecurity.com>
      hdm <hdm@metasploit.com>
    
    Basic options:
    Name      Current Setting  Required  Description
    ----      ---------------  --------  -----------
    EXITFUNC  process          yes       Exit technique: seh, thread, process, none
    LHOST     127.0.0.1        yes       The listen address
    LPORT     4321             yes       The listen port
    
    Description:
      Connect back to the attacker, Inject the meterpreter server DLL via
      the Reflective Dll Injection payload (staged)
    
    
    root@kali ~/metasploit-framework$


###  Arguments are not case sensitive
*Lower/mixed case wouldn't work*

    root@kali ~/metasploit-framework$ ./msfvenom -p windows/meterpreter/reverse_tcp LHOST=127.0.0.1 lport=4321 -o
    ---snip---
    Basic options:
    Name      Current Setting  Required  Description
    ----      ---------------  --------  -----------
    EXITFUNC  process          yes       Exit technique: seh, thread, process, none
    LHOST     127.0.0.1        yes       The listen address
    LPORT     4444             yes       The listen port
    ---snip---
    root@kali ~/metasploit-framework$