stb_truetype: Fixed a memory leak in example code

[Brotcrunsher]

The example code previously created a bitmap via stbtt_GetCodepointBitmap but never freed it, effectively creating a memory leak. This commit calls the proper stbtt free function stbtt_FreeBitmap.

[Brotcrunsher]

As a side note: The example also never calls fclose to the corresponding fopen. This however could be seen as an irrelevant best practice thing which has nothing to do with the topic of the example code: showing stb_truetype.

[nothings]

Yes, the sample code didn't do any cleanup of anything, which was consistent. It also doesn't do any error checking. I thought it was clearly supposed to be throw-away sample code, not cut-and-paste-able sample code, but clearly I was wrong, so I need to rethink this.

[Brotcrunsher]

I volunteer to do this for stb_truetype. If you want this, just name me the scope of the checks:

1.) Should memory leaks be checked?
2.) Should return values be checked?
3.) Should C library functions be handled properly?
4.) Anything else that I miss?

[nothings]

@Brotcrunsher :

I volunteer to do this for stb_truetype. If you want this, just name me the scope of the checks:

1.) Should memory leaks be checked?
2.) Should return values be checked?
3.) Should C library functions be handled properly?
4.) Anything else that I miss?

I appreciate the volunteering, but since the sample code is embedded in the library I need to trade off all of these choices with length, so I have to do it myself I think.