* Remove composite helper functions
* Add set difference and Bitset/uint256 operators
* Convert tests to use new feature bitset set difference operator
In order to automatically run unit tests with newly created
amendments, prefer to start with jtx::supported_features() and
then subtract unwanted features.
These changes identified a few bugs that were hiding in
amendments. One of those bugs, in FlowCross, is not yet fixed.
By uncommenting the test in CrossingLimits_test.cpp you can see
failures relating to that bug. Since FlowCross is not yet
enabled on the network we can fix the bug at our convenience.
Both Tickets and SHAMapV2 have been around for a while and don't
look like they will be enabled on the network soon. So they are
removed from the supportedAmendments list. This prevents Env
from automatically testing with Tickets or SHAMapV2 enabled,
although testing with those features can still be explicitly
specified.
Drive-by cleanups:
o supportedAmendments() returns a const reference rather than
a fresh vector on each call.
o supportedAmendments() implementation moved from Amendments.cpp
to Feature.cpp. Amendments.cpp deleted.
o supportedAmendments() declared in Feature.h. All other
declarations deleted.
o preEnabledAmendments() removed, since it was empty and only
used in one place. It will be easy to re-add when it is needed.
o jtx::all_features_except() renamed to
jtx::supported_features_except(), which is more descriptive.
o jtx::all_amendments() renamed to jxt::supported_amendments()
o jtx::with_features() renamed to with_only_features()
o Env_test.cpp adjusted since featureTickets is no longer
automatically enabled for unit tests.
Enable all supported amendments in Env by default. Rename `features()`
to `with_features()` and add `all_features_except()` to support feature
subsets in Env. Refactor internal feature handling based on a bitset.
