add spec when p is given both argument and block

I decide to change the behavior of p in that case:

p('title'){ titled_block } returns only the result of block.

Although not documented on the spec, p('argument'){ block } returns the Array of the arguments and the result of the block.

I think it's more useful if we could use the argument of p just as the description of the block
modify expression of spec
print_block_with just returns the result of block

Then p just returns the result of block
make sure the subject block executed before each example
delete non-used argument from print_block_with
add pry and rb-readline as development dependencies

pry didn't work on my environment without rb-readline
Merge branch 'arg-and-block'