Add: "include" keyword, allowing to include files without external tools

[glx22]

Many GRF workflows use tools to combine multiple files into a single NML (C preprocessor, python, ...).

So I though it would be nice to be able to do that natively in NML. It's done during parsing by switching lexer data.

I also added optional <ID> = <expression> as include parameters, allowing to replace some parts inside the included file during parsing (very basic equivalent of #define from C preprocessor).

Include syntax is include(<filename>[, <ID> = <expression>[, ...]]);.

Added identifier concatenation support using <identifier>.<identifier>.

--nml output for 042_include.nml:

param[0] = 0;

param[0] = (param[0] + 1);

const _NAMExy = 1;
param[0] = (param[0] + _NAMExy);


param[0] = (param[0] + 2);

const _testxy = 2;
param[0] = (param[0] + _testxy);


param[0] = (param[0] + 3);

const _test2xy = 3;
param[0] = (param[0] + _test2xy);

[andythenorth]

Tested simplest case with FIRS, works as expected.

andythenorth/firs@0beca16

[andythenorth]

Tested locally as working with params.

include("src/polar_fox/cargo_classes/cargo_class_constants.nml", cabbage=2, ham=1);