Add missing readline/history.h include in NuParser

[alebcay]

When building on Ubuntu, we encounter the following errors:

objc/NuParser.m:1009:13: error: call to undeclared function 'read_history'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
            read_history(history_file);
            ^
objc/NuParser.m:1030:13: error: call to undeclared function 'add_history'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
            add_history (line);
            ^
objc/NuParser.m:1092:9: error: call to undeclared function 'write_history'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
        write_history(history_file);
        ^
3 errors generated.
make: *** [Makefile:109: objc/NuParser.o] Error 1
make: *** Waiting for unfinished jobs....

As shown in this example, <readline/history.h> contains read_history, add_history, and write_history.