Delineate intersecting shards

[Sam-Martin]

• Renamed dedupe_policy_shards to dedupe_policy_shard_subsets to differentiate it from delineate_intersecting_shards.
• Added delineate_intersecting_shards to reduce the size of PolicyShards which have conditions whose ARPs intersect with ones without conditions.
  This helps clear up #10
• Improved issubset on PolicyShard to recognise that a shard without conditions CANNOT be a subset of a shard with conditions.
• Added < and > to PolicyShard.
• Updated difference on PolicyShard so that it only adds other's conditions to self's not_conditions if self is allow and other is deny.
• Added documentation on how PolicyShard dedupe works
• Renamed ConditionCollection to RawConditionCollection
• Ensured that Conditions are always treated as a set not a list.
• Ensured that Condition's Operator, Key, Values are always of type ConditionOperator, ConditionKey and ConditionValue.
• Corrected bug in CaseInsensitiveString that caused it to generate case sensitive hashes.
• Added dedupe_result param to difference method on PolicyShard to allow merging of intersecting shards that are not subsets of one another.
• Added intersection to PolicyShard.
• Prevent attempting to calculate the difference between a Deny shard and an Allow shard. Other way makes sense as that's effective permission.
• Updated PolicyShard implementation to Support pydantic 1.9