Feature: read metadata if present

[rouson]

This PR adds the capability to read a metadata JSON object if it is present before the hidden_layers array and formatted as follows:

    "metadata": {
        "modelName": "Network",
        "modelAuthor": "Joe Bloggs",
        "compilationDate": "2023-02-09 16:10:18.544724",
        "usingSkipConnections": false
    },

The corresponding information is used to construct a metadata_t object that is a new component in the inference_engine_t derive type. If no metadata JSON object is found, then the metadata_t component is constructed with empty strings and a .false.. The primary purpose of the new metadata object is to specify whether skip connections will be used between hidden layers.