TargetingTag domain struct

[elpiel]

TargetingTag fields:

• tag: string, arbitrary tag name
• score: Score

TODOs:

• Add fixtures PR Issue #26 TargetingTag #39
• Update ChannelSpec ChannelSpec fields #24 fixture to generate 0+ TargetingTags PR Issue #26 TargetingTag #39
• Custom (de)serialization for handling the score from 0 to 100 validation

Edit:

• Score - number, from 0 to 100

Additional Score struct was created that will handle the scoring and validate 0 to 100 instead of having a _secret: () that guards TargetingTag from not using new fn (which was removed)