Improve write time by using a byte lookup table

[M4GNV5]

Using this patch reduces file write time drastically.
Old startup time: 0.011s, new startup time: 0.382s
Old file write time: 11.938s. new file write time: 0.005s

Thats a 2387.6x speed increase!

Write output to a buffer first before calling write would probably speed this up even further.

Contents of the file i used for testing the speed:

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

Tests were run on an Intel i5-6600K @ 3.5GHz running Debian 9 with Linux 4.9.13-1

This is somehow related to #48 however #48 is actually wrong as for writing a lookup table with 256 entries is enough

[typecasto]

Just for comparison, what are the file sizes of the input/output? Could we do it with 2 bytes instead of just 1?