Makefile improvements

- Respect system/port flags by default.
- Be verbose and do not hide output. This makes it easier to debug a build.
- Remove the "options" target.
- Remove config.mk: just edit the Makefile or override flags if needed.
- dist: no need to clean before packaging files.
- dist: pipe directly to gzip without an intermediate tarball file.
- Define and add a POSIX marker to the Makefile.

README

@@ -8,13 +8,14 @@ different channel buffers, that's actually a feature.
 
 Installation
 ------------
-Edit config.mk to match your local setup. sic is installed into
-/usr/local by default.
+Edit the Makefile or override the flags to match your local setup. sic is
+installed into /usr/local by default.
 
 Afterwards enter the following command to build and install sic 
 (if necessary as root):
 
-    $ make clean install
+	$ make
+	# make install
 
 
 Running sic