simplify Makefile

Due to consideration of POSIX compliance issues config.mk had
to be removed. Configuration variables can be overridden by
environment variables or specified via command line.

Additionally all pretty-printed messages were removed and
built-in rules are used. This also simplifies and purges
the Makefile.

config.mk

@@ -1,34 +0,0 @@
-# st version
-VERSION = 0.0
-
-# Customize below to fit your system
-
-# paths
-PREFIX = /usr/local
-MANPREFIX = ${PREFIX}/share/man
-
-X11INC = /usr/X11R6/include
-X11LIB = /usr/X11R6/lib
-
-# includes and libs
-INCS = -I. -I/usr/include -I${X11INC}
-LIBS = -L/usr/lib -lc
-X11LIBS =  -L${X11LIB} -lX11
-
-# glibc
-CPPFLAGS = -DVERSION=\"${VERSION}\" -D_GNU_SOURCE
-
-# flags
-#CPPFLAGS = -DVERSION=\"${VERSION}\"
-CFLAGS = -Os ${INCS} ${CPPFLAGS}
-LDFLAGS = -s ${LIBS}
-X11LDFLAGS = ${X11LIBS}
-#CFLAGS = -g -std=c99 -pedantic -Wall -O2 ${INCS} ${CPPFLAGS}
-#LDFLAGS = -g ${LIBS}
-
-# Solaris
-#CFLAGS = -fast ${INCS} -DVERSION=\"${VERSION}\"
-#LDFLAGS = ${LIBS}
-
-# compiler and linker
-CC = cc