extract not_valid? method from At#new
interpolate only, use map &:... shorthand
refactor weekday lookup and logic for At.parse
handler default is nil, just check for nil
add invalid At test, fix At#valid? to reflect pass new test
commit #848d771 removed the only call to exception_message, but didn't delete method
Merge pull request #64 from koriroys/kjr/refactors

codebase refactoring
Merge pull request #66 from koriroys/kjr/dead-code

#848d771 removed only call to exception_message, but didn't delete it