Add several configure options for the sake of modularity.

This adds the following configure options:

  --disable-tests         Disable compiling test programs
  --disable-network-tests Disable compiling network-based tests
  --disable-tools         Disable compiling tools
  --disable-examples      Disable compiling examples

Additionally, it adds some code to configure.ac to print out some
information about the current build.  The --disable-network-tests flag
is not yet implemented in testlo.