Remove beta label from version strings.

Also update Copyright / Author info in core module.

Remove CHANGELOG.md as it was no longer up to date.

For release notes, see Github release page:
https://github.com/impress/impress.js/releases

For absolutely every detail, see Github commits page (or `git log`)
https://github.com/impress/impress.js/commits/master

Fixes impress#574

Merge pull request impress#643 from impress/dev

1.0.0-beta1: Merge 2 years worth of work from dev to master!

Highlights

* New plugin based architecture allows adding more features without bloating core src/impress.js file
* Source files are in src/ and compiled into js/impress.js with npm run build. End users should continue to use js/impress.js as before.
* 19 new plugins
* Integrates impressConsole.js by default (press 'P' to open speaker console)
* Markdown support for those that are too much in a hurry to type HTML
* 5 new demo presentations under examples/ show case the new features
* Removes the code that prevented impress.js from running on mobile phones

release version 0.6.0

release 0.5.3

release 0.5.2

release 0.5.1

release 0.5

"bugfix release 0.4.1"

"release 0.4"