- Added memory pools for variable size objects (strings).

- Added memory pools for variable size objects (strings).
  There are three pools; for small, medium, and large objects.
- Extended String object to use memory pools.  Most fixed size char
  array fields will be replaced using string pools. Same for most
  malloc()-ed buffers.
- Replaced "char *urlpath" in request_t with "String urlpath".
- Fixed some printf-like function bugs.