Implement multi-algorithm coin selection

[theanmolsharma]

The current CoinSelector class only implements the Lowest Larger coin selection algorithm. The goal is to implement Branch and Bound coin selection and Single Random Draw selection, then use a waste metric to pick the best selection.

Things to implement in CoinSelector class :

1. selectBranchAndBound()
2. selectSingleRandomDraw()
3. getWaste()
4. update select() in CoinSelector class to call all 3 algorithms, calculate waste for all selections and choose the one with least waste.

References:
Our implementation is very very similar to bcoin's implementation so I suggest reading attemptSelection() and the functions it calls.

[Ayush170-Future]

Since no one is assigned. I'll start working on this.

[theanmolsharma]

Since no one is assigned. I'll start working on this.

This issue is not a high priority. #24 is a higher priority. I'd appreciate if you work on that instead of this.
#24 is a bit more involved issue, so before you start implementing code, I'd like to see a short description of what changes you'd need to make and how you'd do it. In summary, make a plan first.

[Ayush170-Future]

Since no one is assigned. I'll start working on this.

This issue is not a high priority. #24 is a higher priority. I'd appreciate if you work on that instead of this. #24 is a bit more involved issue, so before you start implementing code, I'd like to see a short description of what changes you'd need to make and how you'd do it. In summary, make a plan first.

Okay, I'll start working on it.