color: convert all defined color to lower case named function
lib: say: add two colored words to identify ok/fail
lib: add new functions

get_local_ip() is used to get all non-loopback local IP addresses.

syscmd_stdout() is used to execute a system command, and get it's
output.
doc: add document about color usage
cli: dns: new module used to simplify DNS problem locating

New module, have these features by now:

 - list our DNS servers by name/class
 - flush cache on DNS iterator
 - resolve name / IP each other, which supports DNS server specify

Not implemented features:
 - one-key-diag, super easy tool used to locate DNS related problem
 - trace, alias for "dig +trace ..."
doc: INSTALL: add comments about write config files