function headercase( str ) {
	if ( !isString( str ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be a string. Value: `%s`.', str ) );
	}
	return base( str );
}
Converts a string to HTTP header case.

@param {string} str - string to convert
@throws {TypeError} must provide a string
@returns {string} HTTP header-cased string

@example
var out = headercase( 'foo bar' );
// returns 'Foo-Bar'

@example
var out = headercase( 'IS_MOBILE' );
// returns 'Is-Mobile'

@example
var out = headercase( 'Hello World!' );
// returns 'Hello-World'

@example
var out = headercase( '--foo-bar--' );
// returns 'Foo-Bar'