Start documenting Version API

lib/pragma/migration/version.rb

@@ -2,10 +2,25 @@
 
 module Pragma
   module Migration
-
+    # Represents a version of your API.
+    #
+    # This class is used for comparing and sorting API versions and for holding the migrations
+    # associated to each version.
+    #
+    # Usually, versions are instantiated via {Repository.version}.
     class Version
+      # @!attribute [r] number
+      #   @return [String] the number of this version
+      #
+      # @!attribute [r] migrations
+      #   @return [Array<Base>] the migrations in this version
       attr_reader :number, :migrations
 
+      # Initializes the version.
+      #
+      # @param number [String] the version number (this can be anything comparable with
+      #   +Gem::Version+)
+      # @param migrations [Array<Base>] the migrations in this version
       def initialize(number, migrations = [])
         @number = number
         @migrations = migrations