adding the header and source code files of external library muparser, version 2.2.3

This library will be used to evaluate the kinetic reaction formations defined by the user.
cleaning the code.
adding a test example. This particular benchmark case contains kinetic reactions that is defined by user expressions.

The expression will be evaluated by muparser library during run-time. Code is now underdevelopment.
change the name of the function according the definition.
reading the user defined kinetic rate expression using the old ogs5 data structure.
correctly read in the kinetic rate expression.
correct the comment text.
leaving place for later conversion operation.
adding a new type of kinetic reaction.
define string that will store the kinetic reaction rate expression.
reading the rate expression.
linking the muparser library. Not successful so far.
add the subfolder muparser to the project, and also inlcude the location of the header files of muparser library.
std::max is no longer supported by the VS2013 compiler. Using std::fmax instead.
should not call using namespace here,, because ogsChem is not part of the mu library.
this macro "Max" is no longer used in ogs5. It creates a conflict with the Max definition in mu library. Therefore remove it.
change in the CMakeLists.txt file of muparser library, ask it to produce a library.
add muparser include files to the ogsCUI project.
when linking the ogs6THMC library, include the muparser library.
add a function that is calculating the kinetic rate based on user defined rate expression.