doc 函数增强

[xushiwei]

当前:

>>> doc(os.create)
func(string) (*os.File, error)

>>> doc("os.create")
string

可以考虑加强下 doc("os.create") 这种情况，打印该函数的完整帮助。

[visualfc]

#93
使用godoc获取pkg，如果不为gopkg则直接用原doc输出。

[visualfc]

>>>doc("os.create")
use 'godoc cmd/os' for documentation on the os command 

type File struct {
    // contains filtered or unexported fields
}
    File represents an open file descriptor.

func Create(name string) (*File, error)
    Create creates the named file with mode 0666 (before umask), truncating
    it if it already exists. If successful, methods on the returned File can
    be used for I/O; the associated file descriptor has mode O_RDWR. If
    there is an error, it will be of type *PathError.