Add constructor like `Complex{Float64}`

[hyrodium]

The following MethodError should be fixed.

julia> using Quaternions

julia> Quaternion{Float64}(1)
QuaternionF64(1.0, 0.0, 0.0, 0.0, true)

julia> Quaternion{Float64}(1,2,3,4)
ERROR: MethodError: no method matching QuaternionF64(::Int64, ::Int64, ::Int64, ::Int64)
Closest candidates are:
  Quaternion{T}(::Any, ::Any, ::Any, ::Any, ::Any) where T<:Real at ~/.julia/dev/Quaternions/src/Quaternion.jl:2
  Quaternion{T}(::Real) where T<:Real at ~/.julia/dev/Quaternions/src/Quaternion.jl:13
  (::Type{T})(::T) where T<:Number at ~/julia/julia-1.7.1/share/julia/base/boot.jl:770
Stacktrace:
 [1] top-level scope
   @ REPL[3]:1

julia> Complex{Float64}(1)
1.0 + 0.0im

julia> Complex{Float64}(1,2)
1.0 + 2.0im

[sethaxen]

This should be handled implicitly when #75 is finished.

[hyrodium]

This issue was already solved, maybe by #108:

julia> using Quaternions

julia> Quaternion{Float64}(1)
QuaternionF64(1.0, 0.0, 0.0, 0.0)

julia> Quaternion{Float64}(1,2,3,4)
QuaternionF64(1.0, 2.0, 3.0, 4.0)