contributions by the various authors with active copyright assignment.
* docs/Makefile.am (info_TEXINFOS): Add grub-dev.texi.
* docs/font_char_metrics.png: New file.
* docs/font_char_metrics.txt: Likewise.
* docs/grub-dev.texi: Likewise.
* docs/grub.texi (Internals): Move from here ...
* docs/grub-dev.texi: ... here.
