Data.Thyme.Format: backtrack properly on ambiguous inputs

∙ timeParser was too greedy with %Y; fixes #5.
∙ Backtrack properly when %k, %l and %e succeeds but causes a later failure.
Data.Thyme.Format: skipSpace (and expect endOfInput) only with full input

∙ timeParser itself probably shouldn't gobble up spaces before and after.
tests/sanity.hs: show full IResult on prop_parseTime error
thyme.cabal: bump version to 0.3.0.3