Add a new CI system for Linux/macOS/Windows, Azure Pipelines
Configuration based on https://github.com/crate-ci/azure-pipelines
Since crate-ci defaults to failing the build on clippy errors, forked to:
https://github.com/iceiix/azure-pipelines/tree/clippy
with configurable clippy parameters, to allow disabling the hard failures
(until the underlying causes for the warnings can be fixed).
* Allow erroring clippy float_cmp and unsafe ptrs
* Relax allowed clippy warnings
* Install xcb libraries for -lxcb-shape, -lxcb-xfixes
ice_iix