Add overloads for fld, cld, and div

[sethaxen]

This PR adds overloads for fld, cld, and div, which all return a MethodError on master. The overloads for div are the same ones used by ForwardDiff: https://github.com/JuliaDiff/ForwardDiff.jl/blob/29332b12075e66e056843d3b4207d856f98772b3/src/dual.jl#L287-L291

[codecov-commenter]

Codecov Report

Merging #198 (47df782) into master (c3c96eb) will decrease coverage by 2.90%. The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #198      +/-   ##
==========================================
- Coverage   85.11%   82.21%   -2.91%     
==========================================
  Files          18       18              
  Lines        1807     1529     -278     
==========================================
- Hits         1538     1257     -281     
- Misses        269      272       +3     

Impacted Files	Coverage Δ
src/tracked.jl	88.47% <75.00%> (-3.71%)	:arrow_down:
src/derivatives/broadcast.jl	76.62% <0.00%> (-13.94%)	:arrow_down:
src/tape.jl	55.55% <0.00%> (-9.03%)	:arrow_down:
src/api/hessians.jl	84.00% <0.00%> (-3.50%)	:arrow_down:
src/api/tape.jl	72.22% <0.00%> (-2.78%)	:arrow_down:
src/api/utils.jl	84.84% <0.00%> (-2.06%)	:arrow_down:
src/derivatives/elementwise.jl	77.48% <0.00%> (-1.33%)	:arrow_down:
src/derivatives/linalg/reductions.jl	70.31% <0.00%> (-1.30%)	:arrow_down:
src/derivatives/scalars.jl	95.74% <0.00%> (-0.98%)	:arrow_down:
... and 8 more

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