Add list of examples and clean up index

[wgropp]

Problem

There is no list of examples, even though all examples are numbered, similarly to figures and tables. In addition, the Examples index includes entries for "Example nn.nn: ..." for each of the examples, which is a big block of text (sorted under "Example") in the example index. It would be easier to use if these were in a list of examples instead of in the examples index. Other parts of the example index should be unchanged.

Proposal

Add a list-of-examples to the document, and remove the numbered examples from the examples index.

This required a few changes to buildindices2. Those changes also exposed some limitations in buildindices, and fixing those exposed some problems in formatting some index entries. The PR for this fixes those issues as well.

Changes to the Text

No changes to the body of the text. Adds a list of examples after the list of figures and tables, and cleans up the examples index.

Impact on Implementations

None

Impact on Users

Improves the readability of the standard document

References and Pull Requests

https://github.com/mpi-forum/mpi-standard/pull/1035