Add a way to get the max compressed size

[nemequ]

For lzham_compress_memory, it would be helpful to have a function or macro to get the worst-case output buffer size given a specified input buffer size (basically, lzham's version of zlib's compressBound).

Based on some tests it seems like something around 5 bytes, plus 5 bytes per half-megabyte or fraction thereof… I'm currently using this code, but I can't promise it's right (it was determined empirically based on randomly sized blobs of random data up to 8 MiB).

[richgel999]

Great point, I'm on it!