Obsolete crc32 and use a internal copy

[cptjazz]

The type Crc32 is currently public, but it should not be.
The reasons are that this is a type that is only used as a "helper", and that this library is not dealing with hashing funtions per-se and hence should not publicly expose any.

Since we cannot delete (or internalise) a public type without introducing a breaking change, I marked the type as Obsolete to discourage its use by consumers of this library, and created an internal sealed class InternalCrc32 as internal replacement.

The original Crc32 can go out of service when the next breaking changes are introduced.

[JonathanMagnan]

Hello @cptjazz ,

Thank you for your contribution.

Best Regards,

Jonathan

[JonathanMagnan]

Hello @cptjazz ,

Starting from v1.5.2-beta5, the Crc32 class has been marked obsolete.

There is currently a conflict now with this pull since all projects now use the shared project. You don't need to fix it.

We will add the Internal Crc32 class in a few weeks/months when we will believe it's a good time for a breaking changes.

Best Regards,

Jonathan

[JonathanMagnan]

Hello @cptjazz ,

Starting from the version 1.5.6-beta1, the library is now CLSCompilant.

I will close this pull instead of merging it since I choosing to keep the same class name crc32 instead of adding the internal prefix.

Thank a lot for your contribution,

Best Regards,

Jonathan