Review of the command line interface of NESTML.

[DimitriPlotnikov]

As part of #354 the command line interface was extended to support different options. E.g.:
NESTML hast following options. I invite to test and review it: @jougs and @steffengraber.

usage: The NESTML command line tool can be used as 'java -jar nestml.jar
           <options> path_to_models'. Valid options are listed below:
 -d,--dry-run             Use this option to execute the model analysis
                          only.
 -e,--enable_tracing      Enables tracing of templates which were used to
                          generate C++ code. It can be used for debugging
                          purporses.
 -h,--help                Prints this message.
 -j,--json_log <arg>      Defines the name of the file where the model log
                          will be stored in JSON format.
 -m,--module_name <arg>   Defines the name of nest module which is
                          generated with neuron models. Under thisname the
                          module can be installed in SLI/PyNEST.
 -t,--target <arg>        Defines the path where generated artifacts are
                          stored. The only argument determines the folder
                          where the generated code is stored. E.g.
                          --target ~/my_path

Regarding the json output. If the file doesn't have a .log extension, it is appended automatically by the NESTML-tool. You are welcomed to ask for any additional information I should add to the JSON file (input, output folders, version of the NESTML tool, ...). I just wanted to add only necessary information.

Several example outputs in the case of an error or warning:

1. There is a parse error (in this case the neuron name entry is empty since the model structurally invalid. the tool doesn't create an AST)

[ {
  "filename" : "cli_example.nestml",
  "neuronName" : "",
  "severity" : "ERROR",
  "code" : "NESTML_PARSER",
  "row" : 3,
  "col" : 7,
  "message" : "missing ':' at '\\n'"
} ]

2. Context condition violations (errors and warnings):
   [ {
   "filename" : "sub_example.nestml",
   "neuronName" : "iaf_cond_alpha_implicit",
   "severity" : "WARNING",
   "code" : "SPL_LINE_OPERATOR_VISITOR",
   "row" : 15,
   "col" : 10,
   "message" : "Addition/substraction of real and 1 / ms. Assuming: 1 / ms.(<15,10>)"
   }, {
   "filename" : "sub_example.nestml",
   "neuronName" : "iaf_cond_alpha_implicit",
   "severity" : "WARNING",
   "code" : "SPL_LINE_OPERATOR_VISITOR",
   "row" : 17,
   "col" : 10,
   "message" : "Addition/substraction of real and 1 / ms. Assuming: 1 / ms.(<17,10>)"
   }, {
   "filename" : "sub_example.nestml",
   "neuronName" : "iaf_cond_alpha_implicit",
   "severity" : "WARNING",
   "code" : "SPL_LINE_OPERATOR_VISITOR",
   "row" : 18,
   "col" : 35,
   "message" : "Addition/substraction of real and mV. Assuming: mV.(<18,35>)"
   }]