Simplify arithmetic in wrenStringFind by removing startIndex offset from loop range and using start directly as the initial index. Rename internal primitives to string_indexOf1 and string_indexOf2 for clarity. Add validateIndex helper to clamp negative start values and reject out-of-bounds indices. Update documentation to describe the new start parameter behavior. Add comprehensive test suite for indexOf with start, including negative offsets, edge cases, and error conditions.
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.
Andew Jones
Bob Nystrom
Sven Bergström