DSL implementation stack

[greole]

This PR adds the basic implementation of the NeoFOAM DSL. Its primary design constraint is that should work as simple text replacement to OpenFOAMs DSL.
For example:

fvVectorMatrix UEqn
(
  fvm::ddt(U)
  + fvm::div(phi, U)
  - fvm::laplacian(nu, U)
);

if (piso.momentumPredictor())
{
  solve(UEqn == -fvc::grad(p));
}

would be implementable as

Equation UEqn
(
  implicit::ddt(U)
  + implicit::div(phi, U)
  - implicit::laplacian(nu, U)
  ==
- explicit::grad(p)
);

if (piso.momentumPredictor())
{
  solve(UEqn, U, controlDict);
}

The actual implementation is done within the following PRs.

• init implementation of the DSL #121
• Feat/dsl implementation #127
• DSL coefficients: Implementation of operator coefficient handler  #151
• DSL operators: Implementation of DSL operators #152
• DSL equations: Implementation of DSL Equations #150
• Time integration: Implementation of basic time integration #158
• Documentation: Documentation of NeoFOAM DSL #147

TODO:

• Split equation into expressions, equations. (renamed equation to expression for now)

prior

• Dsl/operator intergration #136

[greole]

This branch doesn't seem right. Can't we just use NeoFOAM::parallelFor here?

[greole]

Replace logic just by a parallelFor?