Use Enum classes for the channel value formats and post processing flags

[LiamOverett-AMRC]

Use Python's Enum class to group the channel value formats and post processing flags.

Doing this groups the two sets of variables into semantically meaningful classes and now the attributes within are commented in a way to show up in IntelliSense. By also grouping this way, the cf_ and proc_ prefixes can be removed to aid in readability.

Code changes:

• Create Enum classes
• Remove comments from original variables and place them under the "Compatibility Interface for old pylsl API" section
• Update examples to use enum classes
• Update examples to no longer use the aliased resolve_stream() function and instead replace with resolve_byprop() where appropriate

[cboulay]

Hi @LiamOverett-AMRC , thank you for the submission.

• this is an API change without much benefit to the user so I won't consider merging it until there are other significant API changes to make it worthwhile for users to update their client code.
• I actually prefer having my type annotations namespaced (i.e., pylsl.StreamOutlet > StreamOutlet).
• Getting rid of resolve_stream usage is welcome and I would be happy to merge a PR that focused only on that.