mmap_read - memory map a file for reading
(const char* filename
mmap_read opens filename
for reading, maps the whole file into memory,
closes the file, writes the length of the file to filesize
a pointer to the mapped file.
The file is unmapped by the operating system if the process terminates. It can
also be manually unmapped by calling munmap
If the file could not be opened or mapped, (void*)0 is returned.