Read past buffer end in lexer

There seems to be a read-past-buffer issue in the lexer. Let's say that you have a file that ends with /, then here you peek behind the end of the buffer. This pattern is used several times. I did not look closer into the potential effects of this pattern but it might lead to crashes if by chance the lexer continues to find valid patterns, I assume.

I just noticed that you set the respective byte to zero explicitly, here. I recommend to add this requirement to the function description of lex or better, to remove this requirement.