We have been tracking down odd error messages when writing data and
found the problem to be internal server errors when writing empty
bodies.
I added fairly comprehensive test coverage for /api/v2/write as well
as simplify and clarify the error messages.
I did this with a dumb editor macro, so some comments changed too.
Also rename root package from platform to influxdb.
In interest of minimizing risk, anyone importing the root package has
now aliased it to "platform" so that no changes beyond imports were
necessary in those files.
Lastly, replace the old platform module to local path /dev/null so that
nobody can accidentally reintroduce a platform dependency while
migrating platform code to influxdb.