Split into ES6 modules (Closes #747)

lib/codemirror.js

package.json

src/banner.js

src/codemirror.js

src/display/Display.js

src/display/focus.js

src/display/gutters.js

src/display/highlight_worker.js

src/display/line_numbers.js

src/display/mode_state.js

src/display/operations.js

src/display/scroll_events.js

src/display/scrollbars.js

src/display/scrolling.js

src/display/selection.js

src/display/update_display.js

src/display/update_lines.js

src/display/view_tracking.js

src/edit/CodeMirror.js

src/edit/commands.js