Setup CI and implement more

[sandersky]

This project uses semver, please check the scope of this pr:

• #none# - documentation fixes and/or test additions
• #patch# - backwards-compatible bug fix
• #minor# - adding functionality in a backwards-compatible manner
• #major# - incompatible API change

CHANGELOG

• Update dependencies to latest versions.
• Configure continuous integration.
• Change minimum Node version to 6.
• Add code of conduct.
• Locked down browser environment so no methods can be overwritten.
• Removed some lazy requires in favor of stricter Flow types (may add a Babel plugin eventually to convert requires to lazy loads automatically).
• Add DOMImplementation, DOMParser, and DocumentType classes.
• Add Flow types to lib directory for consumers using Flow types.