Function starts_with

docopt_util.h:28–34

namespace {
	bool starts_with(std::string const& str, std::string const& prefix)
	{
		if (str.length() < prefix.length())
			return false;
		return std::equal(prefix.begin(), prefix.end(),
				  str.begin());
	}

	std::string trim(std::string&& str,
			 const std::string& whitespace = " \t\n")