This change adds a new informational CIP entitled "Coin Selection
Algorithms for Cardano".

The purpose of this CIP is to describe, in human-readable terms, the
coin selection algorithms currently used by Cardano Wallet and other
parts of the Cardano ecosystem.

The CIP is divided into a number of sections:

The "Background" section:

  * introduces the fundamental concepts behind coin selection;
  * provides a discussion of why coin selection is a non-trivial problem;
  * describes the goals of coin selection algorithms.

The "Interface" section:

  * describes the common interface unifying all coin selection algorithms
    used within Cardano Wallet;
  * describes the standard parameter types, result types, and error types
    used by the common interface;
  * describes the properties that all conforming implementations are expected
    to satisfy.

The "Algorithms" section:

  * gives detailed descriptions of each of the individual coin selection
    algorithms used in Cardano Wallet;
  * gives step-by-step descriptions of the computations involved.

The "Reference Implementations" section:

  * provides links to reference implementations of each algorithm in
    various languages (currently limited to Haskell, but additional
    languages could be added in future revisions).

The "External Resources" section:

  * provides links to other resources useful for understanding issues
    relating to coin selection.

This section describes the motivation for writing this document.

This change also adds a "Scope" section, to clarify and delineate the
scope of this article.

In response to review feedback:

#2 (comment)