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.
I am trying to split the MsgMetadata structure since it is getting
rather big.
Strictly speaking, BodyLength is the property of the body, not message
as a whole. Additionally, keeping it separate creates the possibility of
being inconsistent with the real body size i.e. in case of any changes.
