strings.parser: Add \` aka escaped backtick.

core/strings/parser/parser.factor

@@ -31,6 +31,7 @@ ERROR: bad-escape char ;
         { char: \( char: \( }
         { char: \) char: \) }
         { char: \! char: \! }
+        { char: \` char: \` }
     } ?at [ bad-escape ] unless ;
 
 symbol: name>char-hook

language/backticks/backticks.factor

@@ -4,7 +4,7 @@ USING: fry io io.encodings.utf8 interpolate io.launcher
 multiline sequences ;
 in: backticks
 
-SYNTAX: `
+SYNTAX: \ `
     "`" parse-multiline-string '[
         _ interpolate>string
         utf8 [ contents ] with-process-reader