first step towards log configuration from a string param

- add new zlog init APIs that will get a string as a parameter and
  initialize the log configuration from that string instead from a
  configuration file.
- for now don't parse the string, just use some hard-coded rules.
get the log configuration from a string parameter

- create new API for zlog to initialize the log configuration
  from a string parameter instead from a file.
remove default rule when reading config from string
check the result of parsing the configuration string

- check the return value of zlog_conf_build_with_string.
Merge pull request #1 from airtame/elis_dev

log configuration from string parameter and not configuration file