Clamp Melt Fraction

[aelligp]

This PR clamps the melt fraction functions to values between 0.0 and 1.0. On the CPU there are some Float64 rounding errors that lead to complex numbers when calculating e.g. LinearMeltViscosities

before:

julia> extrema(ϕ)
(0.0, 1.0000000000000004)

Clamping prohibits that ϕ exceeds 1.0, see e.g.:

compute_meltfraction_ratio(args::Vararg{Any, N}) where N = 
clamp(compute_param_times_frac(compute_meltfraction, args...), 0e0, 1e0)

Also some fixes in the docs and adds the icon (CC @boriskaus)

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/MeltFraction/MeltingParameterization.jl	80.00%	4 Missing ⚠️

Additional details and impacted files

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