Various build improvements

I noticed the makefile was a bit empty so modified it a bit:
-Added config.mk, with some sane default like -O2 and a default install prefix
-Linked that to config.mk, which now has install and uninstall and install targets
-Removed makeexec.sh, setuid is just done via chmod
-Whitespace cleanup throughout
-README changes to match the new Makefile.

You obviously don't need the config.mk, but I think it's nice to have all settings in a location separate from the actual Makefile.