Add an extension for #24

This is only a simplified system. A full implementation would need to add support for nested keys, and also support the same set of class libraries that bitser does.

examples/bitser-templates.lua

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+-- this implements a simplified form of binser templates (without nested keys)
+
+local templates_by_identity = {} -- template -> name
+local templates_by_name = {}
+local class_by_templatename = {}
+
+local function bitser_match(value)
+	return value._template ~= nil and templates_by_identity[value._template]
+end
+
+local function bitser_dump(value)
+	local templatename = templates_by_identity[value._template]
+	local template = templates_by_name[templatename]
+	local output = {templatename}
+	local extras = {}
+	for k, v in pairs(value) do
+		extras[k] = v
+	end
+	for i, key in ipairs(template) do
+		output[i + 1] = extras[key]
+		extras[key] = nil
+	end
+	output[#output + 1] = extras
+	return output
+end
+
+
+local function bitser_load(value)
+	local templatename = value[1]
+	local obj = {}
+	local template = templates_by_name[templatename]
+	for i, keyname in ipairs(template) do
+		obj[keyname] = value[i + 1]
+	end
+	for k, v in pairs(value[#value]) do
+		obj[k] = v
+	end
+	return setmetatable(obj, class_by_templatename[templatename])
+end
+
+local function register(class, name)
+	name = name or class.name
+	templates_by_identity[class._template] = name
+	templates_by_name[name] = class._template ---parse_template(class._template)
+	class_by_templatename[name] = class
+	return class
+end
+
+return {
+	registerClass = register,
+	["bitser-type"] = 'table',
+	["bitser-match"] = bitser_match,
+	["bitser-dump"] = bitser_dump,
+	["bitser-load"] = bitser_load,
+}

examples/templates.lua

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+-- how to use the extension API to implement templates ala
+-- https://github.com/bakpakin/binser#templates
+
+local bitser = require 'bitser'
+local bitser_templates = require 'examples.bitser-templates'
+
+bitser.registerExtension('templates', bitser_templates)
+
+local template = {
+	"name", "age", "salary", "email", "nested"
+	--nested = {'more', 'nested', 'keys'}
+}
+
+local Employee_MT = {
+	__name__ = 'Employee_MT',
+	name = "Employee",
+	_template = template
+}
+Employee_MT.__index = Employee_MT
+
+local joe = setmetatable({
+	name = "Joe",
+	age = 11,
+	salary = "$1,000,000",
+	email = "joe@example.com",
+	nested = {
+		more = "blah",
+		nested = "FUBAR",
+		keys = "lost"
+	}
+}, Employee_MT)
+
+bitser.registerClass(Employee_MT)
+print('without templates:', #bitser.dumps(joe))
+bitser.unregisterClass('Employee_MT')
+
+bitser_templates.registerClass(Employee_MT)
+print('with templates:', #bitser.dumps(joe))