FreeTypeFontGenerator to generate single characters

I would like to support other alphabets than latin too, so that is why I cannot generate all required characters in the beginning when my game starts. That's why I created this simple function, that can create Glyph and Bitmap objects for single characters. Then I can use it to update Texture object(s) in my own Font object.

I know many of you will say that this is very slow method, but I've been using this principle both in desktop with C++ and in Android with Java, and I've never had any performance problems with it.

I also added small function that can be used to calculate "real" height of font. This was in older TTF-library (stb-truetype), but I didn't found it from this new one.

And sorry if my coding style is ugly. This is my first pull request ever and Java is kind of new to me too.