add +__if_render.me__+ statement for conditional rendering #29 enhancement "Conditionally render files based on answer.

Variables can also influence rendering. Surround variables with plus signs. 
For example foo/+__if_render.me__++author+/+age+.bob given variables author being Foo and age being 12, foo/Foo/12 will be rendered if render.me is True.

Else only foo/ will be rendered. Please notice that only ('y', 'yes', 'true', 'True', 1) are True, anything else will be considred as False.

it's a proposition for #29 enhancement "Conditionally render files based on answer.