Document parsing and formatting functions. am: 85c3438f06

Original change: https://android-review.googlesource.com/c/platform/system/librustutils/+/2942468

Change-Id: I2d949fc251b3cddbea5da39acc502a1ccf1bb1ea
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>