Move general methods of IntervalBox to IntervalArithmetic

[lbenet]

Fixes #78

[lbenet]

Tests require the corresponding changes in IntervalArithmetics (and probably a tagged version) to pass.

[lbenet]

@dpsanders Shall I go ahead and merge this? https://github.com/JuliaIntervals/IntervalArithmetic.jl/pull/160 has been merged.

[codecov-io]

Codecov Report

Merging #83 into master will increase coverage by 2.12%. The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master      #83      +/-   ##
==========================================
+ Coverage   56.14%   58.26%   +2.12%     
==========================================
  Files          10        9       -1     
  Lines         431      393      -38     
==========================================
- Hits          242      229      -13     
+ Misses        189      164      -25

Impacted Files	Coverage Δ
src/newton.jl	0% <ø> (ø)	:arrow_up:
src/krawczyk.jl	0% <ø> (ø)	:arrow_up:
src/contractors.jl	90% <100%> (-0.48%)	:arrow_down:
src/roots.jl	88.13% <100%> (+2.19%)	:arrow_up:
src/IntervalRootFinding.jl	4.65% <100%> (+2.61%)	:arrow_up:
src/complex.jl	83.33% <66.66%> (+8.33%)	:arrow_up:

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[dpsanders]

Thanks @lbenet !