Additions to Marlowe DSL

[bwbush]

Here are several ideas for additions to the DSL for Marlowe Core:

1. Time arithmetic.
2. Time relative to events, including the start of contract or the minTime.
3. Parameters in Bound (i.e., not just constants), so that bounds can range between variables instead of numbers.
4. Roles as parameters, so that the role in a choice etc. can be a variable.
5. Payment to scripts, which needs the capability to attach datum or datum hash to output.
6. Callable functions.
7. Function for computing a hash of an integer.
8. Bit arithmetic.
9. Mint and distribute new role tokens during the course of a contract, instead of at the beginning.
10. Mint utility tokens during the course of a contract.
11. Fold-based recursion.
12. Iteration and loops.
13. Delete a parameter from the state.
14. Deposit a non-predefined amount
15. Manage tokens together as Value, not separately.
16. Combinators for and and or of Contracts
17. Set payment PKH for a role, so that sending to the payout validator can be bypassed.

[bwbush]

Additionally, early repayment of loans requires interest functions like PV, FV, NPV, etc.