also get rid of mostly unused helper libraries and some stylistic oddities in the MD5 code
I don't know if it's a bug in luajit but on an x86_64 CPU: ```lua > = ffi.cast("uint32_t", 0xFFFFFFFFE) + 0 4294967294LL ``` while on an ARM CPU: ```lua > = ffi.cast("uint32_t", 0xFFFFFFFFE) + 0 4294967295LL ```
to speedup koreader startup for PDF/DJVU documents especially when reflowing