0.4

The 0.4 release brings two new "stress test" functions and also adjusts the cmd list distribution of STM_sequential:

• #415: Remove --verbose in internal mutable_set_v5 expect test to avoid a test failure on a slow machine
• #443: Add Lin_domain.stress_test as a lighter stress test, not requiring an interleaving search.
• #462: Add STM_domain.stress_test_par, similar to Lin_domain.stress_test for STM models.
• #472: Switch arb_cmds to use an exponential distribution with a mean of 10, avoiding lists of up to 10000 cmds in STM_sequential (reported by @nikolaushuber).