Move pic animation documentation to docs/

Move growth rates to a data/ table
Name more SECTIONs

docs/pic_animations.md

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+# Pic Animations
+
+Pic animations are assembled in 3 parts:
+
+- Top-level animations:
+   - `frame` *#*, *duration*: Frame 0 is the original pic (no change)
+   - `setrepeat` *#*: Sets the number of times to repeat
+   - `dorepeat` *#*: Repeats from command *#* (starting from 0)
+   - `end`
+
+- Bitmasks:
+  Layered over the pic to designate affected tiles
+
+- Frame definitions:
+  first byte is the bitmask used for this frame  
+  following bytes are tile ids mapped to each bit in the mask
+
+Animation data is in these files:
+
+- gfx/pics/anims.asm:
+  Main animations (played everywhere)
+
+- gfx/pics/extras.asm:
+  Extra animations, appended to the main animation.  
+  Used in the status screen (blinking, tail wags etc.)
+
+- gfx/pics/unown_anims.asm and gfx/pics/unown_extras.asm:
+  Unown has its own animation data despite having an entry in the main tables.