Adding README.

Change-Id: Ib7542c7a78f747fb7e0b10c7cb9c1e3fc6950bb0

Author: jimbojw

README.md

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+Megaplot is a TypeScript + WebGL engine for implementing high-performance,
+large-scale, interactive data visualizations.
+
+Visualizations rendered with Megaplot are:
+
+* Smooth — Visualizations should not be jittery or laggy and should respond
+  quickly to user interaction. The API should make it easy for developers to
+  carry out expensive operations without locking up.
+* Beautiful — Elements should be superbly designed and rendered with the
+  greatest fidelity afforded by the platform.
+* Fast — Operations should be performed as quickly as possible without
+  sacrificing the quality of the user experience.
+* Big — The engine should be able to handle as much data as the browser can
+  receive and process. Data points should be able to number into the hundreds
+  of thousands without significant degradation.
+* Accessible — Different viewers have different needs. Visualizations made with
+  Megaplot should work for as many users as possible. While ultimately the
+  appearance and functionality of a visualization made with Megaplot
+  depends on the implementer, Megaplot should provide functionality to make
+  it easy for implementers to make visualizations that are widely accessible.
+
+## Megaplot Benefits
+
+Compared to other web-based, data visualization rendering options, Megaplot
+offers these unique benefits:
+
+* Integrated Coordinate Systems — Many rendering environments assume a
+  particular coordinate system (such as 2D pixel space or 3D world coordinates).
+  Megaplot combines world coordinates and pixel coordinates. Objects can
+  have positions in both systems, and these are additive. This allows the
+  developer to achieve previously challenging effects such labels with fixed
+  pixel offsets from particular world coordinates, or size minimums/maximums
+  specified in pixels.
+* Interactive Vector Graphics at Scale — Megaplot is designed to render hundreds
+  of thousands of data objects while still responding to user input. Data is
+  expected to change in response to user interactions.
+* Ubiquitous Interruptible Animations — Sprite attributes are interpolated on
+  the GPU for smooth animations frame-by-frame. Animations are interruptible,
+  with most attributes preserving momentum between changes (no abrupt stop and
+  restart).
+
+In addition to those benefits, Megaplot offers these features:
+
+* Scale - Render hundreds of thousands of datapoints.
+* High Fidelity — Objects rendered by Megaplot have shapes and borders computed
+  on the GPU with vector-graphic precision. No pixelation of curves and other
+  shapes when zoomed.
+* Declarative, Attribute-based API — Each Sprite has a number of attributes
+  which can be set to define its position and appearance.
+* Hit Testing — To support mouse/touch interactivity, Megaplot provides a hit
+  testing API wherein the developer can probe for which objects intersect a
+  particular pixel coordinate of interest.
+* High-Performance Text — In a DOM context, glyphs of text are tiny vector
+  images. While text with fixed coordinates can often be rendered quickly, text
+  that moves can be slow. Megaplot uses a generated Signed Distance Field (SDF)
+  texture for rendering glyphs efficiently at scale, commingled with other
+  visual elements.
+