Allow drawing scaled chars (hagl_put_scaled_char) and text (hagl_put_scaled_text)

[yanickv]

Drawing of text is much too small without scaling (on TTGO T-Display). I tried larger fonts, but were not big enough (and some of the biggest fonts didn't work properly).

[tuupola]

This is related to #39 and #42. I have not decided yet which way to go but it will most likely be style objects. Style objects would allow multitude of different parameters while still keeping the API lean.