Sqlcmd

- Now supports the ipython pyreadline module on Windows, allowing sqlcmd
to work on Windows properly.
- Explicit support for ALTER statement, to permit table completion.

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- "" is no longer an alias for ".load". It's too complicated to support.
- ".load" will now do file-name completion on its argument, including
tilde expansion.
- Made more improvements to tab-completion, especially for dot (".") commands.
- Documented how extended (unrecognized) commands are handled.
- Fixed log handling.
- Some other internal cleanup.

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- Fixed parsing error with the "" command.
- Dot (".") commands now show up properly in help.
- Added tab completion to various commands. For instance:
* ".<TAB>" shows the "." commands
* ".set <TAB>" shows the variables you can set
* ".set variable <TAB>" shows the legal values for the variable
* ".connect <TAB>" shows all the database aliases in the config file
* "select * from <TAB>" shows the tables in the current database.
(So does "select <TAB>", actually.) This works for all SQL commands.
* ".history <TAB>" shows the commands in the history.
".history s<TAB>" shows the names of all commands in the history
beginning with "s"
etc.

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- No longer craps out if $HOME/.sqlcmd/config is missing, but -d (--db)
is on the command line.

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- First version posted to the web.