Add a document for project principles (#1069)

This PR adds a document under `/docs` for project principles as we
discussed in #56. This closes
#56.

Author: qinsoon

docs/contribute/principles.md

@@ -0,0 +1,30 @@
+# Development Principles
+
+These define how we deal with code.
+
+## Why we need principles?
+* They keep the project focused on the right direction.
+* They keep the project disciplined.
+* They make users' expectation for the project clear.
+
+## Principles
+
+* **Enforcability**
+  * Meta-principle. We enforce the principles in a systematic way. We use automated checks to enforce the principles as much as we possible.
+* **Performance**
+  * Our goal is to build high performance memory management systems.
+  * We need to have the tools (for measuring performance) that allow us to create high performance systems.
+* **Flexibility**
+  * Flexibility is a prerequisite to creative, ambitious engineering, and is thus a key principle.
+  * The design should maintain clear abstraction.
+  * Flexibility should not be at odds with performance.   Our motto (from Ken Kennedy): _abstraction without guilt_.
+  * Encapsulation is our key weapon in ensuring flexibility.
+* **Clarity/Accessibility**
+  * Our goal is to provide a toolkit that is widely used.    Consequently:
+    * The code should be clear and easy to understand.
+    * A good programmer (with no GC expertise) should be able to understand the code and make changes.
+    * Use standard coding styles, use standard license, support standard IDEs, etc.
+    * Systems need to work 'out of the box'.
+* **Security**
+  * Our system must be secure.
+  * We should be a platform for research into memory management security.