Support derivative boundary conditions

[ErikQQY]

Fix: #281
Fix: #83
Could possibly unblock #282

with this PR, we can just specify the derivative boundary condition as

function bc!(res, u, p, t)
    res[1] = u(0.0)[1] + pi / 2
    res[2] = u(1.0, Val{1})[2] - pi / 2 # u(1.0, Val{1})[2] is the u2'(1.0)=pi/2
end

[github-actions]

Benchmark Results

	master	9094c05...	master / 9094c05...
Simple Pendulum/IIP/BoundaryValueDiffEqMIRK.MIRK2()	7.94 ± 0.42 ms	7.94 ± 0.27 ms	1
Simple Pendulum/IIP/BoundaryValueDiffEqMIRK.MIRK3()	2.95 ± 0.23 ms	2.93 ± 0.2 ms	1.01
Simple Pendulum/IIP/BoundaryValueDiffEqMIRK.MIRK4()	1.03 ± 0.11 ms	1.01 ± 0.1 ms	1.02
Simple Pendulum/IIP/BoundaryValueDiffEqMIRK.MIRK5()	2.64 ± 0.49 ms	2.61 ± 0.46 ms	1.01
Simple Pendulum/IIP/BoundaryValueDiffEqMIRK.MIRK6()	1.2 ± 0.2 ms	1.19 ± 0.23 ms	1.01
Simple Pendulum/IIP/MultipleShooting(10, Tsit5; grid_coarsening = false)	1.94 ± 0.69 ms	1.9 ± 0.68 ms	1.02
Simple Pendulum/IIP/MultipleShooting(10, Tsit5; grid_coarsening = true)	3.24 ± 1 ms	3.21 ± 1.1 ms	1.01
Simple Pendulum/IIP/MultipleShooting(100, Tsit5; grid_coarsening = false)	0.075 ± 0.019 s	0.0755 ± 0.02 s	0.993
Simple Pendulum/IIP/MultipleShooting(100, Tsit5; grid_coarsening = true)	0.0894 ± 0.02 s	0.0888 ± 0.022 s	1.01
Simple Pendulum/IIP/Shooting(Tsit5())	0.267 ± 0.084 ms	0.267 ± 0.084 ms	1
Simple Pendulum/OOP/BoundaryValueDiffEqMIRK.MIRK2()	9.37 ± 0.44 ms	9.42 ± 0.48 ms	0.995
Simple Pendulum/OOP/BoundaryValueDiffEqMIRK.MIRK3()	3.41 ± 0.24 ms	3.43 ± 0.26 ms	0.994
Simple Pendulum/OOP/BoundaryValueDiffEqMIRK.MIRK4()	1.2 ± 0.11 ms	1.2 ± 0.12 ms	1
Simple Pendulum/OOP/BoundaryValueDiffEqMIRK.MIRK5()	3.07 ± 0.59 ms	3.11 ± 0.59 ms	0.99
Simple Pendulum/OOP/BoundaryValueDiffEqMIRK.MIRK6()	1.44 ± 0.18 ms	1.44 ± 0.19 ms	1
Simple Pendulum/OOP/MultipleShooting(10, Tsit5; grid_coarsening = false)	3.73 ± 3 ms	3.68 ± 3 ms	1.01
Simple Pendulum/OOP/MultipleShooting(10, Tsit5; grid_coarsening = true)	6.17 ± 5.2 ms	6.18 ± 5.3 ms	0.998
Simple Pendulum/OOP/MultipleShooting(100, Tsit5; grid_coarsening = false)	0.134 ± 0.019 s	0.132 ± 0.032 s	1.01
Simple Pendulum/OOP/MultipleShooting(100, Tsit5; grid_coarsening = true)	0.162 ± 0.036 s	0.161 ± 0.032 s	1
Simple Pendulum/OOP/Shooting(Tsit5())	0.654 ± 0.081 ms	0.655 ± 0.12 ms	0.999
time_to_load	5.34 ± 0.035 s	5.29 ± 0.021 s	1.01

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).