Added Makefile for installing libxia and xip

The Makefile at the root directory of this repository invokes the
Makefiles in libxia/ and xip/, and also knows how to install them.
This commit also removes the howto file.
Merge pull request #3 from abreen/master

Add Makefile for installing libxia and xip

The Makefile at the root directory of this repository invokes the
Makefiles in libxia/ and xip/, and also knows how to install them.

This commit also removes the howto file.