WebStory Engine 2017.1

This release comes with the following improvements:

• Custom data sources can now be used (#27)
• Default textbox style changed

It also changes some under-the-hood stuff:

• Remove browserify2using, use usingify
• Change changelog file to markdown format
• Update ESLint config
• Remove MO5.Dict dependency, use string-dict
• Use easy-ajax instead of MO5.ajax
• Remove MO5.dom.Element dependency, use class-manipulator
• Add enjoy-core to the dependencies
• Remove loops, use functions instead
• Savegame feature now refactored into its own module
• Remove attachEventListener (because we don't support legacy browsers)
• Add a createElement module for easier DOM element creation