Rename module rule -> ruler

src/scripts/component/genome-browser.ts

 import SelectedChromosome from "./selected-chromosome";
-import BrushableChromosomeRule from "./rules/brushable-chromosome-rule";
+import BrushableChromosomeRule from "./ruler/brushable-chromosome";
 // D3
 import { select, Selection } from "d3-selection";
 

src/scripts/component/rules/brushable-chromosome-rule.ts → src/scripts/component/ruler/brushable-chromosome.ts

 import { BrushableAxisData, GenericAxisData } from "../../types";
 import { select, Selection, event } from "d3-selection";
 import { scaleLinear } from "d3-scale";
-import GenomeAxis from "./chromosome-rule";
+import GenomeAxis from "./chromosome";
 import { brushX, BrushBehavior } from "d3-brush";
 import { format } from "d3-format";
 

src/scripts/component/selected-chromosome.ts

 // D3
 import { select, Selection } from "d3-selection";
 import { SelectedChromosomeData, GenericAxisData, GeneData } from "../types";
-import ChromosomeRule from "./rules/chromosome-rule";
+import ChromosomeRule from "./ruler/chromosome";
 import Gene from "./sequence/gene";
 import { drag } from "d3-drag";
 

src/scripts/index.ts

-export { default as BrushableChromosomeRuler } from "./component/rules/brushable-chromosome-rule";
-export { default as ChromosomeRuler } from "./component/rules/chromosome-rule";
+export { default as BrushableChromosomeRuler } from "./component/ruler/brushable-chromosome";
+export { default as ChromosomeRuler } from "./component/ruler/chromosome";
 // sequences
 export * from "./component/sequence/gene-shapes";
 export { default as Gene } from "./component/sequence/gene";