* feat(path): added operator= for path_components to keep component type and value synchronized
* fix(path): added missing TOML_EXPORTED_MEMBER_FUNCTION directives
* refactor(path): changed constructors to preserve type - value correlation in path_component
* fix(path): added TOML_EXPORTED_CLASS for path_component
* fix(path): corrected placement of TOML_EXPORTED_CLASS for path_component. urgh.
* fix(path): tidied up some constructors/accessors in path_component