Changed const char* -> string in most of wpilibc.

The HAL will remain untouched in order to maintain C-style
compatibility. A few places in wpilibc were left as
C-style strings, especially if special formatting (eg,
elaborate uses of snprintf or sscanf) was being used.

In general, const char* was changed to std::string.
character buffers used for formatting were either
untouched, changed to std::stringstream, or changed
to std::string, depending on what was done with
the buffer.

Change-Id: I5e431ddf1cc4d9a6d534e1f21b16ea23be26e7f1

wpilibc/wpilibC++/include/Buttons/NetworkButton.h

@@ -14,8 +14,8 @@
 
 class NetworkButton : public Button {
  public:
-  NetworkButton(const char *tableName, const char *field);
-  NetworkButton(::std::shared_ptr<ITable> table, const char *field);
+  NetworkButton(const std::string &tableName, const std::string &field);
+  NetworkButton(::std::shared_ptr<ITable> table, const std::string &field);
   virtual ~NetworkButton() = default;
 
   virtual bool Get();