v3.5.6: Improve private wsKey resolution for futures userData streams, misc fixes, docs updates, util methods

What's Changed

• feat(v3.5.6): Improve private wsKey resolution for futures userData streams, misc fixes, docs updates, util methods by @tiagosiebler in #665
• chore(v3.5.6): bump for release by @tiagosiebler in #666

• chore: force private url for user data sub request
• fix: null value handling in algo order REST response
• feat: inherit util methods around custom order ID generation. feat: intro quickstart guide
• feat: update quickstart guide & tutorial link
• chore: revise quickstart guide phrasing
• chore: docs update, feat: add exchange info util methods for futures
• feat: update tpsl & bracket order examples
• fix: capitalised boolean for algo order priceProtect, aligned with docs
• fix: beautifier edge case with null object guard

Full Changelog: v3.5.5...v3.5.6