Repo cleanup to comply with new catapult deploy process

- Renamed `firepad-min.js` to `firepad.min.js` for consistency with
other libraries
- Added /dist/ folder to `.gitignore`
- Replaced references to version number with `0.0.0`
- Replaced all-release `CHANGELOG.md` with per-release `changelog.txt`
- Removed `release.sh` script
- Added `npm run travis` command to `package.json` to build the
distribution files before testing
- Updated and corrected things in the README
- Updated README build badge to only show state of `master` branch