Enhancements and breaking changes

This release brings a lot of improvements and API changes. The breaking changes are targeted to harmonize the library usage, so similar functionality between the API, Lightstreamer, and Database is called in the same way.

• There is now a single error type (IG.Error) instead of a different error type for each subservice. The error type adopts SE-112 protocols and CustomDebugStringConvertible.
• API and Streamer coalesce the functionality for positions, working orders, and confirmations under the deal subcategory.
• Streamer now support CONFIRM and OPU subscriptions.
• The plural prices is used consistently everywhere.
• The database have now extra functionality counting data points.
• Performance have been improved by reducing the amount of heap pointers within structures (making pure stack structures).
• Better support for non-forex markets.
• The tests have been expanded to better support positions and working orders.