LaTeX.js Files

This release fully supports ES6 modules. LaTeX.js itself has not changed, but the build system and the docs have improved a lot.

exports: - no default export anymore, export: he, parse, Generator, HtmlGenerator

build: - simplified rollup config and build - added visualizer - generate correct source maps - get rid of all eval calls - use dynamic imports for external packages and documentclasses

unit tests: - update to puppeteer 3.3, now we can start to support Firefox screenshots - added a script to create a native LaTeX rendering for the test cases - updated mocha - support and fix code coverage

docs: - moved to VuePress - use a git worktree in the website folder to generate the docs and playground in the gh-pages branch