flexible API

``` ruby
# support path like object that responds to :to_s to get fullpath
Tembed.call Pathname.new('/path/to/font.ttf')

# support multiple paths as arguments
Tembed.call '/path/to/font1.ttf', Pathname.new('/path/to/font2.ttf')

# support array of paths as arguments
Tembed.call ['/path/to/font1.ttf', Pathname.new('/path/to/font2.ttf')]
```
