Make p a functor

[guillaumearm]

conforming to #61, replace p.tmby morph combinator.

example :

const replace = (searchValue, newValue) => content => (
  content.replace(searchValue, newValue)
);

const replaceDollarsByEuros = replace(/\$/g, '€');
p.map(replaceDollarsByEuros).tc('home.common.title');