Internal Balances and Higher Precision

Adds support for and examples demonstrating the different ways developers can utilize ManageUserBalance.
Supports high precision decimals by incorporating the Decimal library

Alpha: Weighted, Oracle, Stable(prototype) Pools and BatchSwaps

Extended pool creation to include Weighted, Weighted2Tokens, and Stable(prototype) pools. Made sample subdirectories for pool creation and swaps. Also added an allowance revocation script for easy allowance testing.

Alpha: WeightedPools and BatchSwaps

Proof of concept implementations of WeightedPool creation and BatchSwaps. The samples/ directory has sample scripts and json files for creating a pool and executing three types of swaps (single hop, multihop, flash swap)