Adds header for string for char[] + string

include/ear/exceptions.hpp

@@ -1,10 +1,11 @@
 #pragma once
 #include <stdexcept>
+#include <string>
 #include "export.hpp"
 
 namespace ear {
   /// thrown if features are used which are not yet implemented
   class EAR_EXPORT not_implemented : public std::runtime_error {
    public:
     explicit not_implemented(const std::string &what)
         : std::runtime_error("not implemented: " + what) {}
@@ -14,28 +15,28 @@
   /// any inputs. This can be caused by an error in the library itself (please
   /// report it!) or something going wrong while building the library. This is
   /// thrown by ear_assert.
   class EAR_EXPORT internal_error : public std::runtime_error {
    public:
     explicit internal_error(const std::string &what)
         : std::runtime_error("internal error: " + what) {}
   };
 
   /// thrown if invalid ADM metadata is encountered
   class EAR_EXPORT adm_error : public std::invalid_argument {
    public:
     explicit adm_error(const std::string &what)
         : std::invalid_argument("ADM error: " + what) {}
   };
 
   /// thrown if an unknown loudspeaker layout is requested
   class EAR_EXPORT unknown_layout : public std::invalid_argument {
    public:
     explicit unknown_layout(const std::string &what)
         : std::invalid_argument("unknown layout: " + what) {}
   };
 
   /// thrown if other invariants on parameters are not met
   class EAR_EXPORT invalid_argument : public std::invalid_argument {
    public:
     explicit invalid_argument(const std::string &what)
         : std::invalid_argument(what) {}