[Fix] Disable plugin action for unexpected syntaxes

[Kristinita]

1. Summary

I make, that GitHub Emoji works only for Markdown syntaxes.

2. Behavior before pull request

If:

    I works in non-Markdown syntaxes, →

    GitHub Emoji prevents me

Example for:

    Python syntax:

        I can't indent block:

3. Behavior after pull request

For:

• Markdown syntax — GitHub Emoji command run,
• Another syntax — command for syntax run.

4. Argumentation

Users don't needs GitHub Emoji for non-Markdown syntaxes, GitHub Emoji prevents them. I want to use Tab for another actions.

5. Testing environment

• Windows 10 Enterprise LTSB 64-bit EN,
• Sublime Text Build 3143,
• GitHub Emoji 1.2.0,
• Latest versions of Markdown syntaxes from section below.

6. Supported syntaxes

1. Default:

   1. Markdown,
   2. MultiMarkdown.

2. MarkdownHighlighting.

3. MarkdownLight:

   1. MarkdownLight,
   2. MarkdownLight.YAML.

4. MarkdownEditing:

   1. Markdown (Standard),
   2. MultiMarkdown,
   3. Markdown GFM.

5. AcademicMarkdown:

   1. AcademicMarkdown,
   2. AcademicYAML.

I doesn't find another non-deprecated Markdown syntax in Package Control.

If these syntaxes exists:

    we need to add them.

Thanks.

[kpym]

To avoid indentation problems you can check my comment in #10. But I agree that it is even better to limit this plugin to markdown only.