Rearranged methods to follow common structure.
Dropped *Range.isReversed
Simplified primitive iterators.
Moved primitive iterators to upper level.
Introduced sequence classes.
downTo functions return sequence instead of range now.
Implemented reversed() in proper way.

- converted it into function
- return sequence values
- implemented for sequences as well
Moved *Range.step() functions to stdlib.
Simpler toString() in ranges.
New structure of range classes.
Added start and end property to generic range.
Adapted code to new structure of ranges.
Added intrinsic properties of ranges and sequences.
Subclassed Float/DoubleRange from iterable (for uniformity).
Subclassed ranges from sequence.
Rearranged methods in ranges.
Inlined getter calls.
Added equals, hashCode and toString to sequences.
Added ComparableRange.
Reformatted.