This prevents `brew` self-calls from interacting with the stickiness of
HOMEBREW_NO_ANALYTICS being persisted to the brew repo and accidentally
disabling analytics permanently when it should have been for just one run,
while restoring the stickiness of an explicit user-supplied
HOMEBREW_NO_ANALYTICS.
- add `HOMEBREW_PRODUCT` global variable
- only differentiate between `/usr/local` and `non-/usr/local` Homebrew
prefixes to avoid sharing sensitive user information
- note if e.g. build errors are occurring under CI
- Add `HOMEBREW_NO_ANALYTICS` variable (this will be how people opt-out
when this is enabled for everyone)
- Add `HOMEBREW_ANALYTICS_DEBUG` variable to output all the analytics
that are sent
- Move Bash analytics code to `Library/Homebrew/utils/analytics.sh`
- Add documentation for our analytics and why/what/when/how and opt-out
- Only official Homebrew commands are reported
- Ruby analytics are now reported in a forked, background process
