MIGRATE/CHANGES.txt need improved Points verbage [LUCENE-7076]

for MIGRATE.txt, we should have some more verbage, maybe examples of how to index/search a 1D integer. maybe even better, it could be done in javadocs and referenced here as well.

CHANGES.txt I think we should organize so it looks more like changes entry for flexible indexing or other similar big changes, and there is a coherent summary of what happened.

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Migrated from [LUCENE-7076](https://issues.apache.org/jira/browse/LUCENE-7076) by Robert Muir (@rmuir), updated Mar 09 2016
Attachments: [LUCENE-7076.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-7076/LUCENE-7076.patch)

Start by reading MIGRATE.txt and the relevant CHANGES.txt entries, then review the LUCENE-7076 attachment and any existing javadocs for flexible indexing. Clarify the intended 1D integer indexing/search examples and the desired changes-summary structure. Done means MIGRATE.txt provides useful guidance and CHANGES.txt gives a coherent account, with javadocs referenced if appropriate.

Written by the indexing model from the issue text.