Third-party notice - commonmark.js

Three source files of @awacloud/office-md are ported from the CommonMark
reference implementation commonmark.js, which is licensed BSD 2-clause:

  src/common.js        (from upstream lib/common.js; the named-entity table
    and the CommonMark URL percent-encoder are now delegated to
    @awacloud/fw and are no longer derived from upstream)
  src/block/parser.js  (from upstream lib/blocks.js)
  src/inline/parser.js (from upstream lib/inlines.js)

The origin is declared in each file's own header. The upstream copyright
notice and BSD 2-clause licence text below are reproduced verbatim from the
upstream repository (https://github.com/commonmark/commonmark.js, file
LICENSE, first section - the section that covers lib/).

The remaining sections of that upstream LICENSE do not apply here: no code
is derived from upstream lib/from-code-point.js (this package's
fromCodePoint wraps the native String.fromCodePoint), and neither the
bench/samples corpus nor the CommonMark spec text is redistributed.

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Copyright (c) 2014, John MacFarlane

All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.

    * Redistributions in binary form must reproduce the above
      copyright notice, this list of conditions and the following
      disclaimer in the documentation and/or other materials provided
      with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.