Require at least extra verbose (-vv) for Cudd_CheckZeroRef()
New init_flags, more supporting documentation and syntax checking

This commit fixes #11 and fixes #12 ; however, it does so indirectly by
changing the names of possible init_flags.  Further, new features are
now present, including selection of init_flags from the command-line.

While the program gr1c offers command-line selection among all possible
init_flags, rg currently requires ALL_INIT.  grpatch provides no -n switch.

There are no plans to backport the bugfix.  The first release in the
0.7 version series is forthcoming, and file formats will be backwards
compatible.

The input specification format no allows any section to be omitted,
e.g., whereas previously missing SYSTRANS was a syntax error.