hoa: add option to output version 1.1

* spot/twaalgos/hoa.cc: Implement the option.
* bin/common_aoutput.cc, doc/org/hoa.org,
doc/org/oaut.org, spot/twaalgos/hoa.hh, NEWS: Document it.
* tests/core/strength.test: Test that.

doc/org/hoa.org

@@ -21,6 +21,13 @@ some information that are useful to better understand the behavior
 of the tools distributed by Spot, and it also look at some lower-level,
 discussing details that are interesting when programming with Spot.
 
+Spot can read files written using either version 1 or version 1.1 of
+the HOA format.  It currently outputs version 1 by default, but
+version 1.1 can be requested from the command-line using option
+=-H1.1=.  Future version of Spot are likely to switch to version 1.1
+of HOA by default, so version 1 can already be requested explicitly
+using =-H1=.
+
 * Format, files, and TωA
 
 Some note about the abbreviation first.  We usually write "HOA format"
@@ -48,6 +55,9 @@ the HOA format, the output may not be exactly the same as the input.
   deterministic" or "deterministic") automata are currently supported
   by Spot.
 
+- Automata using explicit alphabet (introduced in version 1.1 of the format
+  via =Alphabet:=) are not supported.
+
 - The maximum number of acceptance sets used is (currently) limited
   to 32.
 
@@ -672,6 +682,14 @@ particular:
 | =inherently-weak=   | trusted | yes    | as stored if (=-Hv= or not =weak=)          | can be checked with =--check=strength=                           |
 | =colored=           | ignored | no     | checked                                     |                                                                  |
 
+The above table is for version 1 of the format.  When version 1.1 is
+selected (using =-H1.1=), some negated properties may be output.  In
+particular, =stutter-sensitive= is replaced by =!stutter-invariant=.
+The logic of not cluttering the output with all of =!terminal=,
+=!weak=, and =!inhenrently-weak= is similar to the positive versions:
+=!inherently-weak= implies =!weak= which in turn implies =!terminal=,
+so only one of those is emitted unless =-Hv= is used.
+
 ** Named properties
 
 In addition to the bit properties discussed above, a TωA can carry