Add rule to remove leading shell prompt literal $ (#996)

* Add rule to remove shell prompt literals $

Rule added to handle cases where the $ symbol is used in the command,
this usually happens when the command is copy pasted from a
documentation that includes the shell prompt symbol in the code blocks.

* Change files using black and flake8 style check

* Refactor tests and rule

- Refactor test for cleaner test tables
- Removed unnecessary requires_output=True option

README.md

@@ -279,6 +279,7 @@ following rules are enabled by default:
 * `quotation_marks` – fixes uneven usage of `'` and `"` when containing args';
 * `path_from_history` – replaces not found path with similar absolute path from history;
 * `react_native_command_unrecognized` – fixes unrecognized `react-native` commands;
+* `remove_shell_prompt_literal` – remove leading shell prompt symbol `$`, common when copying commands from documentations;
 * `remove_trailing_cedilla` – remove trailling cedillas `ç`, a common typo for european keyboard layouts;
 * `rm_dir` – adds `-rf` when you try to remove a directory;
 * `scm_correction` – corrects wrong scm like `hg log` to `git log`;