add some new make targets

* `release` creates the tarballs
* `test-release` takes the tarballs, extracts them, builds the library
  and tests and runs the tests
* `docs` run doxygen

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

testbuild.sh

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+logfile="../../testbuild.log"
+
+err_out() {
+  tail $logfile
+  exit 1
+}
+
+./bootstrap.sh
+./configure >> $logfile || err_out
+make -j$(( `nproc` * 2 + 1 )) >> $logfile || err_out
+make check >> $logfile || err_out