rust: release 0.3.1

Include all recent changes in a new release for external use.
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
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# Date:      Tue Apr 12 11:25:35 2022 -0700
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# On branch release-0.3.1
# Changes to be committed:
#	modified:   CHANGELOG.md
#	modified:   ittapi-sys/Cargo.toml
#	modified:   ittapi/Cargo.toml
#
