Building on Mac and Linux

[Gleeok]

I've added support in CMake for building the ZScript lexer and parser using Flex and Bison.

Install these tools if you haven't already (https://sourceforge.net/projects/winflexbison/) and add the folder containing win-flex.exe and win-bison.exe to your PATH environment variable. CMake should detect the presence of Flex and Bison and generate the parser files.

If you do not have Flex and Bison, ZQuest will still build fine, but will not be able to compile ZScripts.

Is adding in another 3rd party dependency a good idea? Is it possible to set CMake to build with flex/bison only if the user wants/has it, otherwise just use the current ones from src/parser/ instead?