The intention is to keep to repo root clean while the list of packages
is slowly growing.
Additionally, a bunch of small (~30 LoC) files in the repo root is
merged into a single maddy.go file, for the same reason.
Most of the internal code is moved into the internal/ directory. Go
toolchain will make it impossible to import these packages from external
applications.
Some packages are renamed and moved into the pkg/ directory in the root.
According to https://github.com/golang-standards/project-layout this is
the de-facto standard to place "library code that's ok to use by
external applications" in.
To clearly define the purpose of top-level directories, README.md files
are added to each.
Some parts were implemented in msgpipeline package poorly hooked to some
bits in check/dmarc. Now it is fully in check/dmarc and pipeline code
simply calls two functions.
Also I took that chance to add proper documentation to check/dmarc with
the intention to contribute some parts to the go-msgauth library later.
For quarantined messsages, the Authentication-Results header provides
all information necessary for troubleshooting. When the message is
rejected altogether, there is no information other than opaque 'DMARC
check failed'. With this commit, log message will contain information
about DKIM and SPF checks status and corresponding identifiers.
