Recommend making boost::range a configurable dependency. #5

These helper functions could be protected by #ifdefs or moved to a separate range_support.hpp.

Similarly, when full Range support is not selected by the user, standard container (for the generic collection algorithms) or std::string (for the string matching algorithms) helper adapters should probably be provided... but always with an option to manually disable/deselect.

On this topic, Range adapters should probably also be added for the string matching algorithms.