Seems the default return stack size is too small

[ruv]

Post4 reports error "return stack overflow" when loading:
https://github.com/ForthHub/fep-recognizer/blob/master/implementation/index.fth

In this program include is nested up to 5 levels. Only files are loaded, no program from the loaded files is run.

post4 -r 77 -i index.fth

— fails.

post4 -r 78 -i index.fth

— works fine.

[SirWumpus]

I'm considering making all the stacks dynamic, grow as needed through malloc(). For the JNI build, I've already done this to handle array unboxing on the data stack, but the CLI build the stacks remain fixed size. In particular having a dynamic return stack would more closely resemble how the return stack would grow downwards on a dedicated (embedded) Forth system.