change default file-extension escape char to underscore

scribblings/formats.scrbl

@@ -163,9 +163,9 @@ This can be useful you're managing your project with git. Most likely you'll wan
 
 Pollen relies extensively on the convention of naming source files by adding a source extension to an output-file name. So the Pollen markup source for @filepath{index.html} would be @filepath{index.html.pm}. 
 
-This convention occasionally flummoxes other programs that assume a file can only have one extension. If you run into such a situation, you can  @italic{escape} the output-file extension using the @racket[world:extension-escape-char], which defaults to @litchar{!}. 
+This convention occasionally flummoxes other programs that assume a file can only have one extension. If you run into such a situation, you can  @italic{escape} the output-file extension using the @racket[world:extension-escape-char], which defaults to the underscore @litchar{_}. 
 
-So instead of @filepath{index.html.pm}, your source-file name would be @filepath{index!html.pm}. When this source file is rendered, it will automatically be converted into @filepath{index.html} (meaning, the escaped extension will be converted into a normal file extension).
+So instead of @filepath{index.html.pm}, your source-file name would be @filepath{index_html.pm}. When this source file is rendered, it will automatically be converted into @filepath{index.html} (meaning, the escaped extension will be converted into a normal file extension).
 
 This alternative-naming scheme is automatically enabled in every project. You can also set the escape character on a per-project basis (see @racket[world:current-extension-escape-char]). Pollen will let you choose any character, but of course it would be unwise to pick one with special meaning in your filesystem (for instance, @litchar{/}).
 

scribblings/world.scrbl

@@ -65,7 +65,7 @@ Determines the default HTTP port for the project server. Initialized to @racket[
 
 @defoverridable[server-extras-dir string?]{Name of directory where server support files live. Initialized to @tt{server-extras}.}
 
-@defoverridable[extension-escape-char char?]{Character for escaping output-file extensions within source-file names. Initialized to @racket[#\!].}
+@defoverridable[extension-escape-char char?]{Character for escaping output-file extensions within source-file names. Initialized to @racket[#\_].}
 
 
 

world.rkt

@@ -82,7 +82,7 @@
 
 (define-settable publish-directory-name "publish")
 
-(define-settable extension-escape-char #\!)
+(define-settable extension-escape-char #\_)
 
 (define-settable compile-cache-active #t)
 (define-settable compile-cache-max-size (* 10 1024 1024)) ; = 10 megabytes