Added support for TrueType fonts with symbol character maps (like "Wingdings" and...

Added support for TrueType fonts with symbol character maps (like "Wingdings" and "Symbol"). Characters for these fonts are usually found in the 0xF020 to 0xF0FF range (a Unicode private use area).
There's also experimental support to additionally map these characters into the 0x0020 to 0x00FF range if no characters are mapped in this area. That means that that, for example, Wingdings' pen symbol can be accessed using 0xF021 and 0x0021.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@891181 13f79535-47bb-0310-9956-ffa450edef68