Pyodc

* `pip install pyodc` will now install the C++ backend so `codc` will work immediately.
* The C++ backed is now installable with pip from `odclib`.
* Added `findlibs` and `odclib` as dependencies.
* To force the use of a different `odc` shared library, set the environment variable `ODC_DIR` to the directory containing the shared library. See the [findlibs] documentation for more information.

* Add a new LongConstantString codec which permits encoding constant columns where the constant is a string > 8 characters in length.
* This saves 1 byte per row compared the previous way these columns were encoded.
* A C++ implementation has been added to ODC at the same time, version 1.6.0
* Bumped required ODC version to 1.6.0 for feature parity.
* Decoding data using this codec will work straight away.
* Encoding data with the new codec is disabled by default and can be enabled with the environment variable "ODC_ENABLE_WRITING_LONG_STRING_CODEC=1".
* At some point in a future release, encoding will be enabled by default.

* Accept various new datatypes and tighten datatype selection logic (fixes [ODB-559]):
* Unsigned Integers: uint8 - uint32 (note uint64 is not supported).
* Signed Integers: int8 - int64.
* Float32 in addition to float64.
* Fixed the selection logic for ShortReal2 and ShortReal codecs so the smallest positive normal float32 number `struct.unpack("<f", b"\x00\x00\x80\x00")[0]` can now be used in data.

* Converted to a pyproject.toml based package.

* Fix various warnings:
* Pandas Deprecation warning about `df.dtypes[0]` needing to become `df.dtypes.iloc[0]`.
* Pandas Deprecation warning about converting implicitly converting dataframe column dtype.
* Pandas Future Warning about concatenation with empty or all-NA dataframes.
* "pkg_resources is deprecated as an API."

* Use findlibs instead of custom finder for odc
* Support constant bitfields
* Correct encoding with constant strings > 8 characters in length
* Support pandas native string type
* Fix access to exploded bitfield columns

* Improved github/ci integration

* Fixed [6]: pip install breaks codc

* Fixed [ODB-534]: PyPI package is missing CHANGELOG