Replace the somewhat-recently-added "nothing" item in the tool bar
with the "Fill" tool, which has been converted back from a Magic tool
to a regular tool.
Also, change bash "==" to sh "=" in "if [ ... ]" tests in Makefile.
Also, link to math library (via "-lm") to make sure "max()" is available to
magic tools.
Also, add missing mention of "--newcolorslast" and "--newcolorsfirst" to manpage.
Created Mirror and Flip Magic tools as plugins (except sound); hooks
added to Magic plugin API to allow starter and starter-undo mirror/flip.
Created Fade and Darken Magic tools as plugins.
Moved magic tool sounds to 'magic'.
Added flip and mirror icons to main Tux Paint UI (used to share magic tools')
Created 'tp-magic-config.sh' to get CFLAGS for compiling magic tool plugins.
Improved magic tool plugin API.
Committed some documentation on magic tool plugin API.
