func RegisterFunctions(name string, implementation func() TemplateFunctions) {
	if allFunctions == nil {
		allFunctions = map[string]NewFunctions{}
	}
	allFunctions[name] = implementation
}
Register a set of functions
name: 'namespace' of functions
package sitekit
type TemplateFunctions interface {
	GetMap() map[string]interface{}
	SetInfo(ctx RequestInfo)
}
var allFunctions map[string]NewFunctions
type NewFunctions = func() TemplateFunctions