…corrected.

…New module for converting model to/from JSON.

…into development

…y vector.

- Issue with tearing fixed: Variables are only explicitly solved, if linear factor is a non-zero literal number
  (previously a division by zero could occur, if the linear factor became zero during simulation).
- Issue with unit of tearing variable fixed, if it is a derivative of a variable
  (previously, the generated code for unitless=false was wrong, if the tearing variable was
   a derivative, since the unit was not taken into account).
- Some test models corrected (since leading to errors with the bug fixes).
- simulate!(..):
  o Support DAE integrators, especially IDA() from Sundials.
  o New keyword useRecursiveFactorizationUptoSize=0
  o If log=true, sizes of linear equation systems are listed, as well as whether
    RecursiveFactorization.jl is used .
- Test for RecursiveFactorization.jl added in TestTwoInertiasAndIdealGear.jl
- Tests for multi returning functions added

…if a time-varying variable was present in the evaluated parameters (e.g. states and init values of states). This issue was fixed.

…inear equations can change between simulation runs.

New file TestMultiReturningFunction10.jl tests this feature.

…e derivatives that have units.

- Fixed wrong definition of T in InsulatedRod (HeatTransfer.jl) and in TestHeatTransfer.jl
  and reactivated test of InsulatedRod in TestHeatTransfer.jl.
- Changed default value of simulate!(..) option nlinearMinForDAE from 1 to 10.
- Improved documentation of simulate!(..)

… compilation) for states and iteration variables of linear equation systems.

…ad of assigning to _der_x to simplify the generated code as preparation for the next steps.

- Reactivated linearization tests in TestTwoInertiasAndIdealGear.jl

…te vector