add Begin End ranges

[rafaqz]

its been really annoying me lately that we can't use begin and end in dimensional getindex.

So I'm considering repurposing our exising Start/End types to use as placeholders in ranges to work like begin and end (probably making an alias Begin = Start.

Closes #195

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 73.39744% with 83 lines in your changes are missing coverage. Please review.

Project coverage is 83.01%. Comparing base (9846bfe) to head (5b95090).

Files	Patch %	Lines
src/Lookups/beginend.jl	44.44%	30 Missing :warning:
src/array/indexing.jl	55.73%	27 Missing :warning:
src/Dimensions/format.jl	84.09%	7 Missing :warning:
src/Lookups/set.jl	76.19%	5 Missing :warning:
src/stack/indexing.jl	66.66%	5 Missing :warning:
src/Lookups/indexing.jl	40.00%	3 Missing :warning:
src/Lookups/selector.jl	88.88%	3 Missing :warning:
src/Dimensions/dimension.jl	66.66%	1 Missing :warning:
src/Lookups/lookup_arrays.jl	96.55%	1 Missing :warning:
src/Lookups/utils.jl	94.44%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #585 +/- ## ========================================== - Coverage 83.83% 83.01% -0.83% ========================================== Files 45 46 +1 Lines 4102 4191 +89 ========================================== + Hits 3439 3479 +40 - Misses 663 712 +49 ```

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