Add Game_Config + CmdlineParser + video options - Config 2 of N

[fmatthew5876]

The PR provides the following

• A set of objects for manipulating configuration parameters, including the ability to disable them or lock them to specific values for platforms where it makes sense to do so.
• A Game_Config class for storing EasyRPG configuration
• Beginning support for config file parsing video options via --config -c
• A new CmdlineParser class for command line arguments

[fmatthew5876]

I need to do another round of testing, but this is ready for review now.

[carstene1ns]

Question: Why do we need the new command line parser? Seems like inventing the wheel when there are ready to use alternatives, e.g. CLI11, Lyra, cxxopts.

[fmatthew5876]

We need a command line parser so it's easier to specify options and try to minimize the amount of work for exposing a config parameter between commandline / config file / scene settings.

Whether we use a third party one or write our own doesn't much matter to me. Command line parsing is a simple exercise. Writing one seemed like less work than evaluating all these other options and then getting them to compile on all our platforms.

This one has an unusual interface in that it parses and advances to the next in the same call. So it doesn't fit a traditional loop. This however is the most efficient way to do it and doesn't do any unnecessary extra parsing.

Whatever we choose. It needs to support unicode and case (in)sensitivity the way we use them. It also needs to be able to support the legacy RPG_RT command line options seamlessly combined with more modern ones.

[Ghabry]

Can you rebase this? Not all PR builders work right now.
For cmdline_parser.h and config_parser.h the indent is still off: We don't indent public:/private:. They must move 1 to the left together with the rest.
loadFromConfig and loadFromArgs need a capital L.

The parser seems fairly solid and this entire PR is a good step in the correct direction. The flexibility is needed because we must support the legacy command line arguments. The configuration system also looks well designed (compared to that abomination in libretro ;)).

Because of its cmd+configfile handling I even consider this as a usable replacement for boost_programoptions.