Add a Base.allignment method

[rafaqz]

Currently unit printing doesn't line up the decimal point like most other Numbers do:

julia> [1.99809802u"s" 2.339098; 1.0 2.0u"km/hr"]
2×2 Matrix{Quantity{Float64}}:
 1.9981 s        2.3391
      1.0  2.0 km hr^-1

Thats because Unitful is missing a Base.alignment method:

help?> Base.alignment
  alignment(io, X) returns a tuple (left,right) showing how many characters are needed on either side of an alignment feature such as a decimal point.

Like this:

function Base.alignment(io::IO, x::Unitful.Quantity)
    # This gives us how long a Number is in show - its all on the left
    length = Base.alignment_from_show(io, x)[1]
    # Then get where the alignment of the parent Real:
    left, right = Base.alignment(io, ustrip(x))
    # Then return the left from the parent real, and the right that combines
    # the parents decimal places, and the printing of the units.
    return left, right + length - (left + right)
end

Which fixes printing:

julia> [1.99809802u"s" 2.339098; 1.0 2.0u"km/hr"]
2×2 Matrix{Quantity{Float64}}:
 1.9981 s  2.3391
 1.0       2.0 km hr^-1

This also fixes DimensionalData.jl printing of Unitful.jl lookups, which currently look pretty bad.

See: ggebbie/OceanGreensFunctionMethods.jl#22

I don't currently have time to write up a PR and follow it through, so leaving this here if anyone else wants to, before I forget about it.