add : Lightning Talk orgfile of kansa ruby kaigi
format org
add hello world sample code

ref : https://github.com/mruby/mruby/wiki/Hello-World
add I speaked comment of lightning talk
fix first paragraph name
cp : hello.c
add : mrb_str_new() etc
cp : hello_fix1.c
call method with instance of mrb_value
cp : hello_fix2.c
fix : like String.new()
cp : hello_fix3.c
fix : String#concat
fix : use mrb_intern2()
refactoring document