tp-magic-config man moved to (1)

Magic tool documentation now split into separate files, and referenced
(as a directory) from README, so that users can find docs to any additional
tools (ones not included by default with Tux Paint) that are installed.
Added new --datadir option, to separate path to brushes/stamps/etc. from that of saved files.
Improved docs on where savedir default is.
Made sure --help, man tuxpaint, and OPTIONS docs all covered all command-line options.
Noted SDL_Pango makes locale-specific fonts unnecessary.
Added "--plugindocprefix" option to tp-magic-config, for where docs should go.
Improved plugin API documentation.
Improved layout of man pages a little.

src/get_fname.h

@@ -6,8 +6,14 @@
 #define GET_FNAME_H
 
 extern char *savedir;
+extern char *datadir;
 
-char *get_fname(const char *const name);
+enum {
+  DIR_SAVE,
+  DIR_DATA
+};
+
+char *get_fname(const char *const name, int kind);
 
 
 #endif