use readline if it's enabled.
Merge pull request #674 from mattn/readline

use readline if it's enabled.
wrong stack position for headless case; close #675
fix correct stack postion for headless case
Merge pull request #676 from skandhas/for-675

fix correct stack postion for headless case
minor cosmetic change after #676
add mrb_mod_remove_method/remove_method
add test for Module#remove_method
Merge pull request #677 from skandhas/pr-add-Module-remove_method

Add Module#remove_method for mruby
Fix a wrong comment
Merge pull request #678 from authorNari/patch-1

Fix a wrong comment
Rebuild CRuby based building script without Makefile

Tested CRuby 1.8.6 and 1.9.3

You can see building configuration in build_config.rb
Merge pull request #679 from masuidrive/merge_to_cruby_building_script

Rebuild CRuby based building script without Makefile
Adapter mrbgems documentation to rake system
Merge pull request #680 from bovi/doc-rake

Adapter mrbgems documentation to rake system
Fix documentation for mrbgems
Merge pull request #682 from bovi/doc-rake

Fix documentation for mrbgems
Add documentation for compilation process
Fixed pure ruby mrbgems can't compile and fixed build script wrong variable name
Fix an unnecessary space