doc: add style guide (#746)

* doc: add style guide

* doc: style guide for python and markdown

* doc: consistent use of periods and explicit double quotes in style guide

Co-authored-by: Hussein Farran <hmfarran@gmail.com>

* doc: better define string style in style guide

* doc: add format string literals to style guide

* doc: add HTML, CSS and JS to style guide

Co-authored-by: Hussein Farran <hmfarran@gmail.com>

docs/style.md

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+# Style Guide
+
+## Generic
+
+* This guide can be ignored for data files that are not to be viewed in an editor.
+* 120 character per line for all source files.
+* Avoid white space errors like trailing spaces.
+
+
+## Python Code
+
+* We mostly follow [PEP8](https://peps.python.org/pep-0008/). Read below to see the differences.
+* 120 characters per line. PyCharm does this automatically, other editors can be configured for it.
+* Strings in core code will be `"strings"`. In other words: double quote your strings.
+* Strings in worlds should use double quotes as well, but imported code may differ.
+* Prefer [format string literals](https://peps.python.org/pep-0498/) over string concatenation,
+  use single quotes inside them: `f"Like {dct['key']}"`
+* Use type annotation where possible.
+
+
+## Markdown
+
+* We almost follow [Google's styleguide](https://google.github.io/styleguide/docguide/style.html).
+  Read below for differences.
+* For existing documents, try to follow its style or ask to completely reformat it.
+* 120 characters per line.
+* One space between bullet/number and text.
+* No lazy numbering.
+
+
+## HTML
+
+* Indent with 2 spaces for new code.
+* kebab-case for ids and classes.
+
+
+## CSS
+
+* Indent with 2 spaces for new code.
+* `{` on the same line as the selector.
+* No space between selector and `{`.
+
+
+## JS
+
+* Indent with 2 spaces.
+* Indent `case` inside `switch ` with 2 spaces.
+* Use single quotes.
+* Semicolons are required after every statement.