Support SQLCMD commands

[Sql Quantum Leap]

Add support for SQLCMD commands, such as:

• :r
• :Setvar
• [:] RESET
• [:] !!
• [:] QUIT
• [:] EXIT
• :List
• :Listvar
• :Error
• :Out
• :Connect
• :On Error

Optionally:

• [:] ED
• :Perftrace
• :Help
• :XML [ON | OFF]

Do not do these:

• :Serverlist

These commands are described on the following MSDN page:

sqlcmd Utility

Start with :r and :setvar as they are the most commonly used, especially if using SSDT.

NOTES:

• SQLCMD processes commands and variable substitution per each batch!
• SQLCMD command names are handled as case-insensitive
• SQLCMD commands inside of block comments and string literals are not processed.
• need to also handle -X[1]:
  • Disables ED and !! commands
  • default behavior is to display a warning only
  • if the 1 is also specified, error and exit