Capture build information and print with -version
StatusHandler renders build info
web.StartServing prints listening address
Print flags on status page.
Always print version information when starting up
Explicitly include domain info in build hostname
Date format for build info doesn't include spaces

go 1.0.3 doesn't support spaces in -X linker options.
Add license header to build_info.go
Merge pull request #189 from prometheus/feature/build-info-and-startup-friendliness

Build info and startup friendliness