Fixed uncontrolled format string bug
Switched to C++11. Code largely unchanged.

Compiler flag 'std=c++14' turned out to have several drawbacks:
 * not supported by the version of gcc shipped with Ubuntu 14.04.1,
 which is the target OS
 * clang calls it differently (and distinguishes between -std=c++1y -std=c++1z)
 * it was easy to drop the (few) dependencies on C++14 features,
 compiler support for C++11 is now sufficient to build the package
Fixed typo