Costing, Sizing, new graph-based IR, optimized graph evaluation

Major update with the following new features

• Generation of graph-based IR from SigmaDsl specification (by Scala compiler plugin) (#336)
• New script costing procedure using graph-based IR
• Translation of ErgoTree to graph based IR for costing and optimized execution
• New direct interpretation of graph IR without rewriting reductions (used both for execution of generated cost function and for computing Sigma protocol trees).
• ErgoTree now supports sharing of sub-trees (to reduce serialized size)
• Common Sub-expression Elimination optimization for compiled ErgoTrees
• Lazy && and || logical operations
• Lazy if branches
• first-class lambdas, including nested lambdas
• ZKProof {...} blocks to explicitly specify propositions with Zero Knowledge proving and verification (#236)
• Extended ErgoTree serialization format to include header byte with version and other flags. (#284)
• Constant segregation for optimized script execution(#264)
• Changed HEIGHT type from Long to Int (#335)
• Renamed Array to Coll type at script level (#299)