Add task for generating documentation

.gitignore

@@ -4,3 +4,4 @@
 /pkg
 /Gemfile.lock
 /tmp
+/docs

Gemfile

@@ -4,6 +4,7 @@ gemspec
 
 gem 'rake'
 gem 'rake-compiler'
+gem 'sdoc'
 
 group :test do
   gem 'minitest', '~> 5.2'

Rakefile

@@ -1,5 +1,7 @@
 require 'bundler/setup'
 require 'rake/extensiontask'
+require 'rdoc/task'
+require 'sdoc'
 
 $gemspec = Gem::Specification.load('duktape.gemspec')
 
@@ -23,6 +25,13 @@ end
 Gem::PackageTask.new($gemspec) do |pkg|
 end
 
+RDoc::Task.new(:docs) do |rd|
+  rd.main = "README.md"
+  rd.rdoc_files.include("README.md", "ext/duktape/duktape_ext.c")
+  rd.options << '--fmt' << 'sdoc'
+  rd.rdoc_dir = 'docs'
+end
+
 task :test => :compile do
   ruby 'test/test_duktape.rb'
 end