Support Windows shells such as Powershell

[mxsdev]

Supporting windows shells:

• Provide shell_behavior in execute request, which will be an enum to specify the desired shell behavior.
• If this is unspecified, we try to determine the behavior based on the name, and fallback to sh-like on *nix, dos-lke in windows
• Need to support -o pipefail and -e equivalents on PowerShell, DOS
  • It would appear that this RFC implementation should do the trick for powershell.
• Need to implement functions in command_windows.go for windows to not break on interactive scripts