[Feature] Add support option to accept config file

[Kevan-Y]

• prefix should be -c or --config
• Should accept only .json file
• Ignore all option if -c option is passed

Example:
The config file will be JSON formatted. Use below as an example.

{
  "input": "./docs",
  "output": "./web",
  "future-feature": "should be ignored for now"
}

The command line will be able to do this.

{ 
Option 1: use command line arguments:
python main.py --input ./site --output ./build --stylesheet https://cdn.jsdelivr.net/npm/water.css@2/out/water.css --lang fr

Option 2: use a config file
python main.py --config ./ssg-config.json
}

[lmpham1]

closed with #16