Add CHANGELOG and detailed migration notes to docs/meta/changelog

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Blocks #75, once those docs are merged, the default docs page for Bloop will describe a 1.0.0 which is significantly different from 0.9.x.

To complete:

• Document 0.9.x changes
  • Find the first commit with each 0.9.x version
  • Define the interface of the immediately previous commit for each
  • Describe the delta
  • Apply http://keepachangelog.com/en/0.3.0/
  • include CHANGELOG in MANIFEST.in, README, docs/meta/changelog#Compact
• Detailed migration guide
  • docs/meta/changelog#Detailed
  • Copy headings from Compact changelog
  • Add old/new samples for each change
  • Describe fixed exceptions, or new exceptions with existing code
• Add "Unreleased" section to Compact, outlining Add debug and info level logging #55, Index should validate against a superset of the projection #71

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Commits for each version's release. Next step: git diff 0.9.x 0.9.x+1 for x [0, 12]

• 0.9.13 8c98c06
• 0.9.12 f4dbefd
• 0.9.11 d5311be
• 0.9.10 f36d242
• 0.9.9 632776c
• 0.9.8 d136387
• 0.9.7 d4be1e3
• 0.9.6 819bddc
• 0.9.5 0ae2418
• 0.9.4 3e1cff0
• 0.9.3 fe6849f
• 0.9.2 a083c03
• 0.9.1 4f085a6
• 0.9.0 4f623ba

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Headings from Keep a Changelog, always in this order:

• [Added] for new features.
• [Changed] for changes in existing functionality.
• [Deprecated] for once-stable features removed in upcoming releases.
• [Removed] for deprecated features removed in this release.
• [Fixed] for any bug fixes.
• [Security] to invite users to upgrade in case of vulnerabilities.

Sample changelog

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git diff v0.9.0..v0.9.1 had no public changes. Dropping 0.9.0 from the changelog since the upgrade instructions will be the same as 0.9.1.

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$ git log v0.9.13..docs-rewrite-03 --oneline | wc -l
560