ls command for cbfsclient

There's obviously a lot more that could be done here, but this lets
you look around some.

e.g.

./cbfsclient ls http://localhost:8484/prague/ep-engine
    d      80B  .deps                     (10 descendants)
    d     82MB  .git                      (12,519 descendants)
    d     17MB  .libs                     (15 descendants)
    d    2.9MB  autom4te.cache            (7 descendants)
    d    447KB  config                    (11 descendants)
    d     69KB  docs                      (6 descendants)
    d    8.8KB  dtrace                    (5 descendants)
    d     31KB  embedded                  (9 descendants)
    d    8.6KB  include                   (1 descendants)
    d    457KB  m4                        (54 descendants)
    d    3.1MB  management                (31 descendants)
    d     55MB  src                       (440 descendants)
    d    6.9MB  tests                     (88 descendants)
    d    664KB  tools                     (27 descendants)
    d     17KB  win32                     (6 descendants)
    d    2.7KB  wrapper                   (12 descendants)
    f       0B  .generated_configuration  text/plain; charset=utf-8
    f       0B  .generated_stat-info      text/plain; charset=utf-8
    f    1.4KB  .gitignore                text/plain; charset=utf-8
    f     435B  .mailmap                  text/plain; charset=utf-8
    f     65KB  Doxyfile                  text/plain; charset=utf-8
    f     11KB  LICENSE                   text/plain; charset=utf-8
    f    341KB  Makefile                  text/plain; charset=utf-8
    f     28KB  Makefile.am               text/plain; charset=utf-8
    f    387KB  Makefile.in               text/plain; charset=utf-8
    f    1.1KB  README.markdown           text/plain; charset=utf-8
    f     41KB  aclocal.m4                text/plain; charset=utf-8
    f     42KB  atomic_ptr_test           application/octet-stream
    f     36KB  atomic_test               application/octet-stream
    f    7.5KB  cbadm-online-update.1m    text/plain; charset=utf-8
    f    7.7KB  cbbackup-incremental.1m   text/plain; charset=utf-8
    f    471KB  checkpoint_test           application/octet-stream
    f     15KB  chunk_creation_test       application/octet-stream
    f    128KB  config.log                text/plain; charset=utf-8
    f     77KB  config.status             text/plain; charset=utf-8
    f     14KB  configuration.json        text/plain; charset=utf-8
    f    782KB  configure                 text/plain; charset=utf-8
    f    8.0KB  configure.ac              text/plain; charset=utf-8
    f    135KB  dispatcher_test           application/octet-stream
    f     967B  ep.la                     text/plain; charset=utf-8
    f     970B  ep_testsuite.la           text/plain; charset=utf-8
    f     34KB  gen_code                  application/octet-stream
    f     58KB  gen_config                application/octet-stream
    f    191KB  hash_table_test           application/octet-stream
    f     31KB  histo_test                application/octet-stream
    f     20KB  hrtime_test               application/octet-stream
    f     904B  libblackhole-kvstore.la   text/plain; charset=utf-8
    f     892B  libconfiguration.la       text/plain; charset=utf-8
    f     954B  libcouch-kvstore.la       text/plain; charset=utf-8
    f     877B  libdirutils.la            text/plain; charset=utf-8
    f     874B  libkvstore.la             text/plain; charset=utf-8
    f     895B  libobjectregistry.la      text/plain; charset=utf-8
    f     895B  libsqlite-kvstore.la      text/plain; charset=utf-8
    f     874B  libsqlite3.la             text/plain; charset=utf-8
    f    299KB  libtool                   text/plain; charset=utf-8
    f     874B  libvslemul.la             text/plain; charset=utf-8
    f     11KB  misc_test                 application/octet-stream
    f    490KB  mutation_log_test         application/octet-stream
    f     18KB  mutex_test                application/octet-stream
    f     18KB  pathexpand_test           application/octet-stream
    f     20KB  priority_test             application/octet-stream
    f     16KB  ringbuffer_test           application/octet-stream
    f     48KB  sizes                     application/octet-stream
    f     944B  timing_tests.la           text/plain; charset=utf-8
    f    502KB  vbucket_test              application/octet-stream

Closes #68