Precompile common workflows

[jishnub]

Some examples:
On master

julia> @time @eval roots(Fun(sin,Interval(big"0.0", big"1.0")))
  6.249275 seconds (19.64 M allocations: 1.002 GiB, 8.53% gc time, 99.67% compilation time)
1-element Vector{BigFloat}:
 2.590850566528333387615905558840119871334800109330884415507111041050577540894939e-77

julia> @time @eval DefiniteIntegral()*Fun(Chebyshev(), [0,1])
  0.487484 seconds (1.18 M allocations: 65.425 MiB, 25.34% gc time, 98.12% compilation time)
0.0 anywhere

julia> @time @eval sin(Fun());
 31.251794 seconds (67.79 M allocations: 3.706 GiB, 4.99% gc time, 99.92% compilation time)

This PR

julia> @time @eval roots(Fun(sin,Interval(big"0.0", big"1.0")))
  3.415315 seconds (3.21 M allocations: 165.702 MiB, 1.46% gc time, 99.02% compilation time: 45% of which was recompilation)
1-element Vector{BigFloat}:
 2.590850566528333387615905558840119871334800109330884415507111041050577540894939e-77

julia> @time @eval DefiniteIntegral()*Fun(Chebyshev(), [0,1])
  0.147715 seconds (217.09 k allocations: 13.275 MiB, 94.74% compilation time)
0.0 anywhere

julia> @time @eval sin(Fun());
 10.228372 seconds (4.80 M allocations: 242.355 MiB, 0.59% gc time, 99.78% compilation time: 29% of which was recompilation)

This comes at the expense of increased precompilation time, and a somewhat larger cache, but that's probably acceptable.

Still WIP, more calls to be added.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.16 ⚠️

Comparison is base (fcfe37c) 70.71% compared to head (064594d) 70.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
- Coverage   70.71%   70.56%   -0.16%     
==========================================
  Files          29       30       +1     
  Lines        2667     2670       +3     
==========================================
- Hits         1886     1884       -2     
- Misses        781      786       +5     

Impacted Files	Coverage Δ
src/ApproxFunOrthogonalPolynomials.jl	81.48% <ø> (ø)
src/precompile.jl	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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