C++ using in header files

[jnohlgard]

Some (most) of the header files in curlcpp have multiple using statements in the first lines of the file, this pollutes the top level namespace with standard library classes and curlcpp classes in user application files which simply want to use include curlcpp as a library and defeats the purpose of the namespace.

The solution would be to move any using statements to the innermost scope, or to remove them altogether.

See also: http://julipedia.meroh.net/2013/12/header-files-avoid-c-using-directives.html