Update version #
Update readme.md
Make PowerShell ExecutionContext available to C#
Qualified positional parameters
Removed most cmdlet aliases; left in place ones based on legacy command line utils (mkdir, rmdir, del)
Spelled out parameter names (ErrorAction instead of ea, Recurse instead of r or re)
Update version number to 13
Add color support for an error status message
Add ValidateAndAcceptLine function

To avoid cluttering the screen and history with command lines
that don't work because of stupid errors like "command not found",
you can bind enter to ValidateAndAcceptLine.
Make Enter default to ValidateAndAcceptLine
Update changes.txt
Add -ValidationHandler for ValidateAndAcceptLine

To support custom validation, for e.g. to allow someone
to reject command lines where arguments are not valid,
you can now specify a custom validation handler script block.
Static validation: don't complain about "-?" or things that use $args.

(rough draft: still need to check for [CmdletBinding()] on other things,
etc.)