Try to support more fonts. Closing: #12

What the PR does:

• Try to show all fonts listed by fc-list.
• Use pango format to print out texts if the default failed. Pango suppoprts special fonts like color emojis better.
• Show available glyphs in the font file (by showing charset with fc-query command) if the font does not cover printable ascii characters. PREVIEW_TEXT is not respected in this case. Also happens a lot for color emojis.

Issues for now:

• The format of color emoji fonts is usually a mess. E.g., it does not break the line where I tell it to.
• I am not familiar with either font configuration for convert, pango, or fontconfig. The problems include:
  • Some font files have more than one font family or style in it, so should I specify fonts with font file or font family-style?
  • Some fonts show multiple families and styles with fc-query. I don't know which one to show, or to show all of them.