Add support for chromium and fuschia package manifest "README"

Some metadata and readme files are structured or semi-structured. We could parse them to extract package-liceke information and declarations.

See https://github.com/fuchsia-mirror/third_party-libvpx/blob/master/README.fuchsia and this: https://src.chromium.org/viewvc/chrome/trunk/src/third_party/README.chromium.template

Another example: https://chromium.googlesource.com/android_tools/+/9a70d48fcdd68cd0e7e968f342bd767ee6323bd1/sdk/platform-tools/systrace/catapult/telemetry/third_party/tsproxy/README.chromium

Some more and
https://github.com/qt/qtwebengine-chromium/blob/b45f07bfbe74c333f1017810c2409e1aa6077a1b/chromium/third_party/PRESUBMIT.py

See also AUTHORS, and various METADATA files:

Some pointers:
https://github.com/search?q=filename%3Areadme.chromium&type=
https://github.com/search?q=filename%3Areadme.facebook&type=
https://github.com/search?q=filename%3Areadme.google&type=
https://github.com/search?q=filename%3Areadme.thirdparty&type=
https://github.com/search?q=filename%3Areadme.android&type=
https://github.com/search?q=filename%3Ametadata.bzl&type=
https://github.com/search?q=filename%3Ametadata.json&type=
https://github.com/PixelExperience/external_libaom/blob/ten/README.version
https://github.com/PixelExperience/external_libaom/blob/ten/README.android