Move `pageChanged` event name into events.js

[sfal]

Fixes #460

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 62.52%. Comparing base (dd08f52) to head (56fa294). Report is 1213 commits behind head on master.

Files with missing lines	Patch %	Lines
src/js/BookReader/Mode2Up.js	20.00%	2 Missing and 2 partials :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #461   +/-   ##
=======================================
  Coverage   62.52%   62.52%           
=======================================
  Files          36       36           
  Lines        3712     3712           
  Branches      705      707    +2     
=======================================
  Hits         2321     2321           
+ Misses       1123     1121    -2     
- Partials      268      270    +2     

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[iisa]

hi @sfal thanks for taking this on. since you have a PR of this fix already, let's push to get this done. can you:

1. rebase and resolve the branch conflict
2. show and confirm that the event is properly firing by screen recording or unit test:

Quick how to screen record:

• run local dev server
• go to dev console and add in an event listener to the event BookReader:pageChanged that will output console.log('page has changed', e) when the page turns
• grab a screen recording of it and make a gif showing the dev console output as the page turns (this is a relatively easy tool to do that: https://ezgif.com/video-to-gif)

[sfal]

Hey @iisa thank you. Here's a gif showing the event is emitted. The quality got really poor when going from video to gif, hope it's still good enough to understand what is happening.