Add `Monad.Maybe.maybe/3` function
Change order of function definitions
Change order of tests
Add `Monad.Maybe.from_just/1` function
Rename variable
Add `Monad.Maybe.from_maybe/2` function
Merge branch 'feature/from-maybe' into develop
Add `Monad.Maybe.maybe_to_list/1` function
Add `Monad.Maybe.list_to_maybe/1` function
Add `Monad.Maybe.cat_maybes/1` function
Simplify macro expansion

There is no need to expand return statements: `return` can just be
imported into the local scope. Thanks to Peter Minten (pminten)
for the hint.