1. Excluded pgfont from Font.fontmap-items; it was used in helppage.lua to render footer and just duplicated ffont
2. Fixed typo: self.cfont > "cfont" in Font:getFace()
3. 3 small functions to change font face for any member of Font.fontmap
* Since fontchooser is replaced by selectmenu, it
is no longer needed. So I rewrite it into font.lua
module which can cache faces that shared among all
UIs.
* add progressBar method in graphics.lua to draw
reading progress.
* add reading progress information in reading menu.
It is just a demo. Should be clean up in next release
when the real reading menu is out. :)