Added a better configuration file + more options

[raphael-dick]

Selected options are stored in the 'svg-inliner.json' file. The file is located in the directory the command was executed. On startup the values are loaded from the file. If a value does not exist in the configuration file. The user has to select the desired value. When the command is executed from a different directory you will have to re-configure the tool.

Update to existing options:

• Export format
  exportType: react_component/string

Added options:

• Toggle HTML Documentation output:
  createHtml: true/false
• Directory where icons are located:
  iconsDirectory: <path relative to directory of execution>
• Directory where export files will be created:
  exportDirectory: <path relative to directory of execution>

[raphael-dick]

Sample 'svg-inliner.json' file:
{ "createHtml":true, "exportType":"react_component", "iconsDirectory":"/icons", "exportDirectory":"/export" }