Scriptconfig

Fixed
* Added workaround for issue with pickle-ability

Added
* New method: `to_omegaconf`
* Experimental `dataconf` and `DataConfig`

Changed
* Can now pass cmdline as a kwargs dict.
* Added support for `required=True`

Fixed
* Issue with custom parsers and tracking "explicitly given"

Changed
* Added type information
* Doc improvements

Added
* `smartcast` can now disable splitting by specifying `allow_split=False`
* Broken: Added `required` as an option to `Value`.

* The `short_alias` keyword to `Value`, which allows single '-' prefix chars on
the command line.

* The `port_argparse` method which takes an existing (simple) argparse CLI and
attempts to make a scriptconfig version of it.

Changed
* The `alias` keyword no expands a single argparse argument instead of making
multiple of them.
* Make numpy optional

Added
* Can now specify alias for a Value as a `str | List[str]`.

Changed
* Arguments can now be specified as both positional and keyword. The keyword
variant will always take priority.

* Changed the way arguments are smart-casted when specified on the commandline

Fixed

* Bug when setting a value to None via the command line

Added
* The `cmdline` argument of `Config` can now be the actual argument string used
on the command line. This will be parsed with shlex and converted to an argv
list.

Fixes
* Fixed issue where `_read_argv` would try to smartcast items where the default
class attribute had a `Value`.


Changed
* The Value object now has a side effect free `cast` method that is called by
`update` when the default value is changed or when handling raw data outside
of the Value object itself.