Add button glyphs to the small font.

[chyyran]

What's changed?

This adds the A B X Y L R Up Down Left Right glyphs to the small font for use in dialogs. This does not affect the large font.

The following glyphs were replaced without substitute with the private use glyphs.

CENT SIGN	    
POUND SIGN
PLUS-MINUS SIGN
DIVISION SIGN
DOUBLE PRIME
POSTAL MARK

The following glyphs were replaced, but could be substituted with the new BUTTON_(LEFT|UP|RIGHT|DOWN) private use glyphs

LEFTWARDS ARROW
UPWARDS ARROW	   
RIGHTWARDS ARROW	   
DOWNWARDS ARROW

Where have you tested it?

Nintendo DSi.

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Pull Request status

• This PR has been tested using the provided devkitPro, devkitARM, and EasyGL2D.

(Do not edit after this point)

• This PR is fully documented.
• This PR has been tested before sending.
• This PR follows C style and convention.