When a fiber is started for the first time via call() or transfer(), the value argument is now bound to the fiber's function parameter if it takes one. Previously, the first value was always ignored. Also adds runtime error for fibers created with functions taking more than one parameter, and updates documentation and tests accordingly.
- Replace string concatenation with interpolation in class method examples
- Remove backticks from Fiber class references in concurrency docs
- Add guidelines for choosing between getters and empty-parentheses methods
- Clarify block syntax for single-expression functions and chaining
Restructure the documentation hierarchy to prepare for documenting additional built-in modules. Move all core library documentation from `doc/site/core/` to `doc/site/modules/core/`, rename `modules.markdown` to `modularity.markdown`, remove `^category` metadata lines from all affected pages, update cross-reference links to use relative paths under the new structure, and add a TODO placeholder to the Class class page.
