v0.4.0

rewrite to make invalid states impossible to represent

previously RangeOrCell had a ton of different combinations and had
some possible invalid states if you used a mix of from=RowRelative and
to=ColumnRelative or vice versa. This splits the RangeOrCell into
more distinct states where you can't mix a row or column reference.
This came with a lot of other implications and nice to haves:

• iterators for iterating the cells or rows between a range. the rules
  are different for each type but intuitive

• Into and AsRef implementations for efficiently converting values
  between the types. the general rules:

  • Things at the bottom (most specific) of the tree (Adress, Column
    & Row) can .into() upwards to a RangeOrCell or an A1

  • AsRef to access the underlying rows or columns without allocating.
    When possible functions take an AsRef<Column> which can be either
    a Column or Address

• Dedicated Row and Column types which can implement Ord, Eq,
  PartialEq and lots of other useful algebraic traits

• support for non-contiguous ranges. "A1", "A:B", "C:C" for example

• contains() actually works (inclusively)

• no more need for builders. with all the different new fns and from
  and into impls there isn't really a need for a builder pattern