Add darwin support

[zchee]

log/syslog module has been supported darwin on current Go stable version (1.6).
Not ignored darwin.
https://github.com/golang/go/blob/master/src/log/syslog/syslog.go#L5

If fix +build linux darwin for
https://github.com/google/logger/blob/master/logger_linux.go#L14
,but can not build by the build file structure of Go.

So, I create a new logger_darwin.go.
If it is not the correct way, please point out.

In addition, If need a sign-off of google to special license(CLA?), I willing to sign.

[zchee]

BTW, I successful go build, but actual behavior is not tested.
Sorry.

and, If need add Linux and Darwin notes on

• https://github.com/google/logger/blob/master/README.md#L3
• https://github.com/google/logger/blob/master/logger.go#L15

, I will also commit.

[adjackura]

+build linux darwin should work fine if you rename logger_linux.go to logger_syslog.go.

Head over here to sign the CLA:
https://cla.developers.google.com/about/google-individual

[zchee]

@adjackura got it.
I will fix and sign later.

[adjackura]

Don't worry about the CLA, looks like you signed it a year ago.

[zchee]

@adjackura Rename and add darwin for +build flag.
PTAL.

CLA: I got it. Thanks.

[zchee]

@adjackura Thanks :)