* Added check for yearday
* Changed some test dates to check different equivalence classes of
yearday (before leap day, at leap day, after february in leap year,
after february in non-leap year)
add tests to ttime.nim for timeinterval add/subtract functionality
Changed assert to doAssert in ttime.nim
Added extra tests to ttime.nim
Removal of singular help procs for working with TimeIntervals
Added TimeIin proc toSeconds(a: TimeInfo, interval: TimeInterval) where subtracting a year gave wrong results
Add overflow of units on initInterval eg, 65 seconds is 5 seconds and 1 minute
