Display IdOffsetRange fields

[jishnub]

While #179 is still undecided, this is a stop-gap (and hopefully less disputed) solution. In my experience displaying the axes of an OffsetArray is necessary more in debugging than anything else, and having the offsets printed makes life easier. This makes interpreting the axis span a little trickier, but it's possible to get used to this.

After this PR:

julia> a = zeros(3:4, 3:4);

julia> axes(a, 1)
OffsetArrays.IdOffsetRange(1:2, 2)

It's always possible to convert these to UnitRanges wherever necessary:

julia> UnitRange.(axes(a))
(3:4, 3:4)

[codecov]

Codecov Report

Merging #193 (90f2af5) into master (b20b4db) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #193   +/-   ##
=======================================
  Coverage   99.28%   99.28%           
=======================================
  Files           5        5           
  Lines         280      280           
=======================================
  Hits          278      278           
  Misses          2        2           

Impacted Files	Coverage Δ
src/axes.jl	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b20b4db...90f2af5. Read the comment docs.

[timholy]

Not a fan, unfortunately. Let's do some variant of #179 (it doesn't have to be Pairs syntax, the key is directly specifying both the axes and the values).