This patch adds two new "make install" arguments:

LIBDIR to specify path for library (/usr/lib by default)
DESTDIR to prepend a path for all installed files as used by packagers
(default is none).

E.g. "make install DESTDIR=/tmp/dest LIBDIR=/usr/lib64" will install:

/tmp/dest/usr/include/csnappy.h
/tmp/dest/usr/lib64/libcsnappy.so

So one can collect /tmp/dest/ content and distribute it as tar
archives or any other pre-compiled package.

Signed-off-by: Petr Písař <ppisar@redhat.com>