Added endianness support.

- Version is now at 0.2.2;
- Compiler will always compile on big endian mode;
- Added flags to force compiling on other endiannesses
(big, little, system-based) (Closes #12).
- Script: Header now has a field "endianness" that stores
the compiled script's endianness. Swapping is not needed
for reading it, as it is an uint8_t (Closes #11).
- Switched names of compiler version variables on script
header;
- Script header now has version defines for better tracking.