How can I open a hidden file in Text Wrangler?
You can use the terminal : 

open ~/path/to/.YourHiddenFile -a /Application/YourApplication.app


The hidden file are hidden by adding a dot in the beginning of the file name.

Or with the good old GUI method : 


Launch the application you wish to use to edit or view the hidden
file.
Select ‘Open’ from the application’s File menu.
An Open Dialog box will display.
With the dialog box as the front-most window (you can click once in
the dialog box to make sure it’s in front), press command + shift + . 
The dialog box now will display any hidden files or folders within
its list items.
You can toggle between the hidden files and folders being displayed
by pressing command + shift + . again.