Define one or more exceptions that algorithms can throw in operator() and flush()

[philiprodrigues]

We should define some exceptions (or maybe just one) that algorithms can throw if they cannot continue. This will give some debugging information to the caller of operator() or flush(), if nothing else.

[philiprodrigues]

I guess the simplest option is something like:

class triggeralgs::algorithm_error : public std::runtime_error
{
   algorithm_error(const std::string& what);
}

Are there other classes of error we might want to model with different exceptions? I haven't thought of any yet