Consolidate "next steps" files into single "todo" file

The project had two files, "bugs" which was version tracked and "todo"
which was not. However, the two files had very similar contents. This
commit merges them (without too much curation) and switches the
version-contolled filename to "todo"

Should probably move most of these to github issues or whatever.

todo

@@ -0,0 +1,77 @@
+Top Priorities
+--------------
+1. Rewrite collation. Right now the algorithm depends upon knowing the pixel
+   extent of each axis, but that shouldn't be necessary and is only marginally
+   an artifact of the implementation. Collation should return a hash with keys
+   being pixel padding and values being the min/max. This would also allow for
+   negative paddings values (for offset text).
+2. Perform dataset collation when datasets are created or changed.
+3. Use SizeSpecs to configure all distances.
+Sliders for interactive plots:
+  - add as option to function plots
+  - add as separate group of options (like palette, axes, legend)
+  - would need to be able to configure their scaling, min, max, and default
+New scaling types:
+  - date scaling type, mostly used (I suspect) for axes
+  - power-law (quadratic, square-root, etc), probably mostly used for color maps
+Add margin/padding options
+Better color space support, use Maggie's ColorSpace?
+
+
+Next Steps: Aesthetics
+----------------------
+1. Use SizeSpecs to configure all distances.
+2. Add margin/padding options
+3. Superscripts and/or subscripts
+4. Better handling of large numbers (depends upon previous)
+5. Better color space support, use Maggie's ColorSpace?
+6. Support legends
+7. Greater configuration for placement, orientation, and size of color map
+8. Fancier axis rendering options, especially background gray
+
+Wishlist
+--------
+Sliders for interactive plots:
+  - add as option to function plots
+  - add as separate group of options (like palette, axes, legend)
+  - would need to be able to configure their scaling, min, max, and default
+New scaling types:
+  - date scaling type, mostly used (I suspect) for axes
+  - power-law (quadratic, square-root, etc), probably mostly used for color maps
+
+Histogram blows up when its data is removed
+colors do not appear to be threading (11-03-08/plot-dists.pl)
+legends
+criss-crossing lines for high zoom levels (maybe need to change Prima
+	interface to use double instead of int)
+
+Colors
+======
+Switch to using Maggie's ColorSpace
+
+Emphasizing Data
+================
+Teach DataSets how to emphasize and de-emphasize their data
+Teach Palettes how to emphasize and de-emphasize their colors
+
+Legends, Color Bars
+===================
+One legend entry per data set
+Auto-detect features based on explicit DataSet properties
+Zoom/pan on color bar emphasizes data in that color range
+
+Grid/Matrix
+===========
+To speed up rendering, work with images
+If grid bounds are within viewport, or extend just outside, use a single
+	Image.
+If grid bounds are much larger than viewport, work with tiles of Images that
+   cover slightly beyond the current view.
+ - Create function/method that updates the tiles one data-row or column at a
+   time. This will preserve user interaction while still updating the plot
+ - When panning (say) left, once the leftmost tiles pan far enough, simply
+   move them to the far right.
+
+On zoom, create first "image" of zoom based on a zoom-in of the current
+	image or tiles. Then use the UI rendering method to improve resolution.
+Might want to create a whole new Prima image class for this