doc/api-keys.texi (Keys): Add note about support of ECDSA

* doc/api-keys.texi (Keys): Add note about support of ECDSA keys with
  GCrypt.
ssh/log.scm (set-log-verbosity!, get-log-verbosity): New procedures

* ssh/common.c (log_verbosity): Move to `ssh/log.c'.
* ssh/common.h, ssh/server-func.c, ssh/session-func.c: Update.
* ssh/log.scm (set-log-verbosity!, get-log-verbosity): Export.
* ssh/log.c (guile_ssh_set_log_verbosity_x)
  (guile_ssh_get_log_verbosity): New procedures.
* ssh/log.h: Update.
* doc/api-logging.texi: Add descripton of `set-log-verbosity!' and
  `get-log-verbosity'.
* NEWS: Update.
* tests/log.scm ("set-log-verbosity!", "get-log-verbosity"): New TCs.