Custom font generator does not support backslash character
When using the custom font generator, the backslash (unicode 0x5C) character value in a font will generate invalid java source code in the icons enum, specifically:

`xxx_icon_name('\u005c'),`

which is equivalent to (in the java compiler):

`xxx_icon_name('\'),`

this escapes the end quote character.

the proper code generated should be:

`xxx_icon_name('\\'),`

Using two unicode codes ('\u005c\u005c') does not seem to work, at least in IntelliJ IDEA, so the double backslash literal is provided as the suggested solution.
