This commit makes passing compile UI tests optional, allowing the CI to
succeed even when UI tests fail. This change was made because UI tests
are highly susceptible to false negatives due to benign rustc compiler
output changes. A failure resulting from such a benign change inhibits
progress in the main branch due to failing PR testing which would have
otherwise passed.
The 'FromFrom' derive now allows type generics in all positions using
the same automatic discovery technique as with 'Responder'. (In fact,
the technique was created for this derive.) Furthermore, 'FromForm' can
now be derived for unit structs.
Also adds a new 'try_with' form field validator.
Resolves#1695.
Sergio Benitez