Updated the function reference document.

* Fixed the description of strncpy().
* Added some [commented out] function names to the lists for some headers.
Merge pull request #119 from greg-king5/strncpy-doc

Update the function reference document.
Updated the CBM error tables.

* Added more mappings between DOS and C codes.
* Changed generic error messages into specific ones.
Merge pull request #120 from greg-king5/cbm-errors

Update the CBM error tables.