Add bitbucket git support.

doc/mrbgems/README.md

@@ -23,6 +23,9 @@ A remote GIT repository location for a GEM is also supported:
 
 	conf.gem :github => 'masuidrive/mrbgems-example', :branch => 'master'
 
+	conf.gem :bitbucket => 'mruby/mrbgems-example', :branch => 'master'
+
+NOTE: ':bitbucket' option supports only git. Hg is unsupported in this version.
 
 ## GEM Structure
 

tasks/mruby_build_gem.rake

@@ -24,6 +24,8 @@ module MRuby
     def load_external_gem(params)
       if params[:github]
         params[:git] = "https://github.com/#{params[:github]}.git"
+      elsif params[:bitbucket]
+        params[:git] = "https://bitbucket.org/#{params[:bitbucket]}.git"
       end
 
       if params[:git]