Project sanity check (#76)

* tslint: CRLF -> LF

* gitignore more build artifacts

* Add proposed .editorconfig

* Allow for "clean" builds

src/ts/generated/ content is still required (sprites.ts,
gamepad-mappings.ts), but src/scripts is not.

* Add --sprites option to production build

* Add note about sprites to README

.editorconfig

@@ -0,0 +1,14 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+
+[*.{js,ts,md,pug}]
+indent_style = tab
+
+[*.json]
+indent_style = space
+indent_size = 2