Render true and false tags in mustache templates

[queenstdev]

Render a template with a boolean value e.g.:

auto t = crow::mustache::compile(R"---({{true_value}} and {{false_value}})---");
crow::mustache::context ctx;
ctx["true_value"] = true;
ctx["false_value"] = false;
auto result = t.render_string(ctx);
CHECK("true and false" == result);

results in a std::runtime_error "not implemented tag type..."

The expected boolean rendering can be seen in the Mustache demo page

[mrozigor]

On the demo page booleans are used with conditional (?) {{#TAG}} tag, not with displaying one {{TAG}}.

[queenstdev]

@mrozigor, you are correct. The default template doesn't have a {{tag}} that is a boolean value.
What I meant to say was that if you use the demo page to render a boolean tag e.g. {{empty}}, it will render false.