Added support for tags

[przemyslaw-zan]

Suggested merge commit message (convention)

Feature: Added support for tags. Closes #148.

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Additional information

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[pomek]

A few notes without scanning the code:

• It would be good to exclude repositories checked-out tags from push, pull, commit, and close commands.
  • push:
  • pull:
• What the L symbol stands for?
  • I would go with @ or T (tags). L (latest) does not mean anything in the entire context of the status command.
• mrgit save produces invalid results now.

  "ckeditor5-dev": "ckeditor/ckeditor5-dev@latest#dccbeb5"

  • mrgit save --branch fails even for repositories with no tags.
  • Everything works fine on master.

[pomek]

mrgit save --branch fails even for repositories with no tags.

It creates the following entry: "ckeditor5-dev": "ckeditor/ckeditor5-dev#HEAD (no branch)" when checked-out tag.

But it can be extracted into a follow-up issue.