Embedded-SGP 6.0.0

* [`changed`] Move the i2c init call out of `probe()` and into the examples
* [`changed`] Faster `sgp30_measure_raw_blocking_read` for FS1.0+. Now 25ms
              instead of 200ms.
* [`changed`] CFLAGS: Enable strict aliasing warnings by default, add `-Os` to
              SGPC3.
* [`changed`] Avoid the use of a 64b temporary when converting absolute humidity
* [`changed`] Split out `default_config.inc` from Makefile to configure paths
              and CFLAGS for SGP30, SGPC3 and SVM30 drivers
* [`changed`] Only one example with either `hw_i2c` or `sw_i2c` is built,
              depending on `CONFIG_I2C_TYPE`. Defaults to `hw_i2c`.
* [`removed`] No longer support SGP30 with feature set < 1.0
* [`changed`] Update submodule to increase timeout while clock stretching in
              software I2C mode
* [`fixed`]   Run `make prepare` in the `embedded-sht` directory when makeing
              the `release` target in order for the `release/svm30` target to
              succeed.
* [`removed`] Remove the `AUTHORS` file from the driver and the
              `embedded-common` submodule, as it adds more noise than benefit.
              The contributors can be found in the git log.
* [`fixed`]   Copy correct `CHANGELOG.md` and `LICENSE` files to target
              locations when running the `release` target of the driver's root
              Makefile.
* [`fixed`]   Fix `cpp` build of SVM30 due to missing header file
* [`changed`] Don't use variable-length arrays (improves portability)
* [`changed`] Change the quite complicated feature set handling code to easy to
              understand constants for SGP30 and SGPC3
* [`changed`] Change the SGP30 error code `SGP30_ERR_UNKNOWN_FEATURE_SET` to
              `SGP30_ERR_UNSUPPORTED_FEATURE_SET`
* [`added`]   Add `SGPC3_ERR_UNSUPPORTED_FEATURE_SET` as error code for SGPC3
* [`removed`] The SGP30 and SGPC3 drivers no longer checks if a measurement was
              started when reading a measurement, in order to remove all global
              static variables
* [`changed`] Move the code documentation from the source files to the headers
* [`added`]   Add error codes `SGP30_ERR_INVALID_PRODUCT_TYPE` and
              `SGPC3_ERR_INVALID_PRODUCT_TYPE` to SGP30 and SGPC3 drivers,
              respectively.
* [`fixed`]   SVM30: Fix calculation of absolute humidity at very low
              temperatures (< -20°C / -4°F). The conversion now bounds the
              result to the lowest result from the look-up table.
              Also become tolerant towards accepting negative %RH values.
* [`fixed`]   SVM30: Fix disabling of humidity compensation at values < 0.08%RH
* [`changed`] SVM30: Better approximation error when calculating absolute
              humidity from relative humidity and temperature
* [`fixed`]   SGP30: Adjust timings according to datasheet
* [`added`]   SGPC3+SHTC1 combo driver in `shtc3_with_shtc1` directory