Add dependency for ext-mbstring, as suggested by @IronLady in #92

[skip ci]

Scrutinizer fixes

Close  #289

* upstream/develop:
  Added PHP version badge

* origin/master:
  Ask if a self-signed certificate is being used. [skip ci]
  Add issue and pull request templates.
  Update inline comments for hook.php and getUpdatesCLI.php Make sure that logging is set directly after Telegram object initialisation. (thanks @jacklul for pointing this out) Proofread and update utils.md file.
  Update readme and examples for enableAdmin(s) and add an extra test for string numbers.

Add new helper method entitiesArrayToJson.

Extract code for setting up the request params into a new function.