Add InfluxDbWriteable procedural derive macro

[msrd0]

Fixes #19

[msrd0]

The InfluxDbWriteable macro should now be working. I don't know if a InfluxDbReadable macro makes sense and what the use case would be? Maybe someone could give an example how they'd like to use it

[Empty2k12]

CI is failing with

README.md out of date. Run "cargo readme > README.md" and commit again.

[msrd0]

@Empty2k12 I've fixed the readme. Kcov is still failing with an error message I cannot understand. Do you have an idea how to fix kcov?

[Empty2k12]

I would guess this is due to you changing the folder structure, resulting in a different folder structure inside the target folder which the kcov command relies on.

[Empty2k12]

How does the new release process work, again?

I release influxdb_derive first, then update influxdb to it's version and release influxdb?

[msrd0]

From my PoV, this PR is ready to be merged. Releasing will go just like you said ... release the derive crate first, wait a minute to give crates.io time to process the new/updated crate, and then release the main crate which has the derive crate as its dependency. However, note that there is no need to update the derive crate if no changes were made, just don't update the version either. It might be a good idea to keep major/minor versions in sync, at least that's what bigger libraries like diesel seem to be doing.

[Empty2k12]

Before releasing I will probably fix #54 to improve behavior on embedded platforms.

[Empty2k12]

LGTM 👍