Prepare Stackless 3.7

[akruis]

Time to prepare Stackless 3.7.

1. Merge branch 'master' into 'master-slp' up to commit 1e17d4a.
2. Start branch 3.7-slp
3. Merge branch '3.7' into '3.7-slp' up to v3.7.0

[akruis]

I'm going to change the "Stackless version" to "3.7". Keeping it at "3.1b3 060516" makes no sense at all.

[akruis]

I'm mostly ready with the preparation of Stackless 3.7. Still to do:

• Merge pull request Stackless issue #198: Improve the soft-switchable extension functions #198
• Merge pull request Stackless issue #188: enable soft switching for sub-iterators, (async) generators and coroutines #188
• Merge pull request Stackless issue #197: stackless call method "contextvars.Context.run" #197
• Merge pull request Stackless issue #199: stackless call "asyncio._CTask" #199
• Merge pull request Stackless issue #192: use tp_finalize instead of tp_dealloc for tasklet finalisation #194 (issue tasklet, channel: use tp_finalize instead of tp_dealloc for complex finalisation code #192)
• Merge pull request Stackless issue #201: enable stackless calls of "wrapper_descriptor" #201
• Merge pull request WIP: Stackless issue #202: remove the STACKLESS_DECLARE_METHOD magic #202
• Merge pull request WIP: Stackless issue #203: use the macro _PyStackless_TRY_STACKLESS #203
• Create branch "3.7-slp"
• Merge upstream commits from branch "3.7". For the largest part this is already done in https://github.com/akruis/cpython/tree/slp37

Once this is done, I can prepare a release.

[akruis]

I just pushed 3.7-slp with tags v3.7.0-slp and v3.7.1-slp. The tests of v3.7.2-slp are still running.

[akruis]

Source code of v3.7.2-slp is available on stackless.com.

Within the next days I'll build the Windows binaries and the Conda versions.

[akruis]

Windows artefacts are available on Stackless.com.