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
Fix an unnecessary space
Merge pull request #683 from bovi/doc-compile

Add documentation for compilation process
Merge pull request #684 from bovi/tiny-beautify

Fix an unnecessary space