* Change 'add' to add to .gitignore by default.
Also add _message() function and improve output from 'git-secret-add',
alter tests for new code behavior, and update docs.
* change tests since 'add' always adds to .gitignore
* improve output: prepend more message with 'git-secret:'.
* update man page for git-secret-add
There are a lot of changes, multiple things were refactored: tests,
some commands, building and meta.
Several critical bugs fixed.
Changes:
1. Fixed#74, when `_user_required` was not working after reimporting keys
2. Closes#73, now it is possible to provide multiple emails to the `killperson` command
3. Closes#72, now it is possible to provide multiple emails to the `tell` command
4. Closes#71, now every doc in this project refer to `git-secret.io` instead of old `gh-pages` website
5. Closes#70, now installation section is removed from main `man` file
6. Closes#69, now "See also" section in the `man`s are clickable
7. Closes#61, added "Manual" section to the manuals
8. Refs #38, added `centos` Dockerfile, but `ci` testing is still failing
9. Refs #52, tests are refactored. Added `clean` command tests, removed a lot of hardcoded things, moved tests execution from `./temp` folder to `/tmp`, added a lot of new check in old tests, and some new test cases
10. Refactored `hide` and `clean` commands to be shorter
11. `shellcheck` is now supported with `make lint`
Additional features are not comming to 0.2.2 after this commit.
