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Remove docs for enqueue_task

See merge request inducer/pyopencl!105

Merge branch 'master' into 'enqueue-task-docs', add comment on adverse effect of pyproject.toml on pypy

# Conflicts:
#   .gitlab-ci.yml

Remove pyproject.toml before pypy CI build

See merge request inducer/pyopencl!104

Add Device.hashable_model_and_version_identifier, deprecate Device.pe…

Add Device.hashable_model_and_version_identifier, deprecate Device.persistent_unique_id (closes gh-327)

Add pyproject.toml

Ensure prg  context availability

See merge request inducer/pyopencl!103

Fix slow import of pyopencl

Multiple ORed values in CONSTANT_CLASSES.to_string

See merge request !100

Wait for Array.events in more places (elwise, reduction, scan, algorithms)

See merge request inducer/pyopencl!102

Remove Py2.5 **dict(x=y) kwarg workaround

See merge request !101

This is mostly implemented for `clGetKernelArgInfo` [1] called with
`CL_KERNEL_ARG_TYPE_QUALIFIER`. Since an argument can have multiple
type qualifiers (e.g. `const` and `volatile`), this returns the bitwise
or of the flags that we need to separate.

[1] https://www.khronos.org/registry/OpenCL/sdk/1.2/docs/man/xhtml/clGetKernelArgInfo.html

Add missing handling of cl.kernel_arg_info.TYPE_QUALIFIER

See merge request !99