minor memory bug fix in mkpool routine

See merge request !17

- scanf string field width modifier does not count null terminator

- in preparation for using json-c and/or bedrock instead

make string long enough for two chars and terminator

implement json configuration

See merge request !16

file backend module

See merge request !13

- eventually need to handle conditional compilation of bake back ends

- avoids potential HG encoder corruption if backend function fails and
  does not populate output fields

fix addr leak in create_write_persist ult

Closes #20

See merge request !12

- fixes #20

Refactoring to enable generic backend interface

See merge request !11