feature: add typescript support

[Skona27]

Changes:

• added typescript declaration file containting typings Slider component
• change in webpack build process - added copy-webpack-plugin in order to copy declaration files to build directory,
• bumped library version to 2.1.0

I recommend using Prettier for this project. I had difficulties to format webpack.config.js file, didn't know if I should use tabs with width 8 or 7 or 6. I decided to format this with my default settings. Please tell me how I can correct this.

[erichbehrens]

Thank you @Skona27 !

The project is configured to use eslint. AFAIK prettier should be able to pick up eslint settings, but I have to admit I stopped using it because of some issues with that and eslint/tslint alone work much better in my case.

Currently the indentation is set to tabs. I'd ask you to push again with tabs, so it is clear what has changed in the config file for this PR. I have already compared it ignoring whitespace and it looks good. I'll later change this setting to spaces as it seems to be far more common.

[Skona27]

Hi!
I've indented webpack.config.js with tabs, so now it should be clear what have changed.

[Skona27]

@erichbehrens Any updates on the subject?