#bem Root-key (base) can be "b__e" and treat undefined as true

[askirmas]

Related: #30
For verbosity

const icon = {"material-icons": true} as const
const ripple = "mdc-ripple-upgraded" as const
const {button__icon, button__ripple, button__lable} = {} as MyClassNames

<button {...bem({button: "raised", [ripple]: "background-focused"})}>
  <span  {...bem({button__ripple})}/>
  <i  {...bem({button__icon, ...icon})}>bookmark</i>
  <span  {...bem({button__label})}>Contained Button plus Icon</span>
</button>

Thus becomes similar to naming

classnames[R]?	value	naming	bem
-	undefined	R	?R
+	undefined	C	?C
-	false	? R | delete R	? R | delete R
+	false	? C | delete R	? C | delete R
-	true	R	R
+	true	C	C
-	string	value	R R--value
+	string	!R, value | C | Error	C C--value
-	null	?delete R	?delete R
+	null	?delete R	?delete R
-	primitive[]	?	R R--value?
+	primitive[]	?	C C--value?
-	{[k]: string}	?	R R--key--val
+	{[k]: boolean}	?	C C--key?