Add additional developer docs from Eclipse Wiki

specifically, adding - API policy - Extending Memory Analyzer - Index
files - MAT capabilities - Reading data from heap dumps

Author: jasonk000

dev-doc/API_policy.md

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+# Memory Analyzer API Policy
+
+This document provides the current API Policy for Memory Analyzer.
+
+## Purpose
+
+Eclipse MAT is built on top of the Eclipse IDE framework, and the components can
+be embedded inside other deployments. As an OSGI framework-capable runtime,
+the components export known consistent APIs that allow other developers and
+components to work together within the IDE.
+
+For example, the [Eclipse MAT Calcite Plugin](https://github.com/vlsi/mat-calcite-plugin)
+plugs directly into the Eclipse IDE and interacts with the Eclipse MAT
+components to enhance its functionality.
+
+## Declared API
+
+The declared APIs in Memory Analyzer are provided as public and documented. The
+API compatibility between different versions of Memory Analyzer should be
+reflected by the version numbers, following the [Eclipse versioning policy](https://github.com/eclipse-platform/eclipse.platform/blob/master/docs/VersionNumbering.md).
+
+## Some examples
+
+- Changes to the API - adding new APIs or deprecating APIs should be documented
+and communicated to the community (e.g. via GH issue and/or mailing list).
+
+- Deprecated API should be available for at lease one major release.
+
+## Provisional and internal API
+
+Provisional APIs should be used while development is occurring. If successfully
+adopted, they might become declared APIs. If not, they can be removed. In any
+situation, the community should be notified.
+
+## Tooling
+
+See the [Contributor Reference](Contributor_Reference.md) for some notes on API
+tooling and configuration.