consolidate build scripts, reorganize source into src/ directory, fix favicon injection

src/shims/btime.js

@@ -0,0 +1,4 @@
+// Obsidian wraps this in try/catch: try{this.btime=window.require("btime")}catch(e){}
+// Returning null causes graceful degradation. mtime is used instead.
+
+export const btimeShim = null;