Rename-Many: allow the user to escape the pattern with a leading back tick

[plastikfan]

Currently, the user can escape a pattern by using the esc, function. But this is quite clumsy to use because you can't just invoke the function, you have to warp it in brackets before doing so, otherwise powershell will take esc as though it were part of the pattern. So instead of this:

... -Pattern $(esc('blah'))

the user should now be able to do this:

... -Pattern '`blah'

[plastikfan]

Can't use a back tick because that has a special meaning inside powershell string, so use a tilde instead.