The travis clang-8 reports a SIGILL with the code:

    std::string str = "    ";
    Ensures(baryonyx::left_trim(str) == "");

Fix the problem using .empty() instead of operator==.

- travis:
  - use `-O2` seems to fix a segfault in the testlib unit test.
  - execute test with gdb

Error seems to unrecognize the ``[[maybe_unused]]` token with the `if
constexpr`:

error: expected unqualified-id before ‘[’ token

     debug_logger([[maybe_unused]] const std::string_view name) noexcept

lib/src/itm-common.hpp:1796:18: error: expected ‘)’ before ‘[’ token

     debug_logger([[maybe_unused]] const std::string_view name) noexcept

                 ~^

The new `cycle` option allows to cycle between every constaint order
option from `none` to `pi-sign-change`.

w is now a real and follows the rules:

- [0..1]: defines a percentage of limit loop where the kappa is not
  used. For example -p w:0.5 -p limit:100 gives 50 loop without kappa
  computation and 50 with kappa computation.

- > 1: defines a static number of loop without kappa computation. For
  examples -p w:50 -p limit:-1 gives 50 loop without kappa and +oo with
  kappa computation.

The value of each variables in the solution/initial vector is
initialized according to the init-policy-random parameter of the
bernouilli's law:

- 1 use the init-policy algorithm to affect 0 or 1.
- 0 use the toss up algorithm (init-random parameter and the
  bernouilli's law) to affect 0 or 1.

trying to merge new idea

to merge with bqp

Add into solvers and core API a BQP mode in objective function.