Minor updates

Major updates:

- add number of tries option
- resolved issue with multiple instances (https://github.com/robiveli/js-captcha/issues/15)
- code improvements
- options more organized
- readme improvements
- demo updated
- add basic unit test with Jest
- drop support for IE10

v1.2.1: Minor update

Read me update regarding defining callback function for success and error messages

v1.2.0: Minor updates

Dev packages updates
Drop support for IE9
Readme update
Main js renamed and included in package for imports

v1.1.1: Minor updates:

- dev dependecies
- properly invoke setCaptcha() method
- readme demo url
- demo adjustment for https://github.com/robiveli/js-captcha/issues/2

v1.1.0.1: Minor updates:

• applied captcha font size to be default in relative rem unit
• applied strict mode
• public api miscs