Revolt Plugin Refactored

[caronc]

Description:

Related issue (if applicable): #1057

Refactored the Revolt plugin to allow markdown to work. Refactoring also allows multiple channels to be specified on the Apprise URL:

• revolt://bot_token/channel
• revolt://bot_token/channel1/channel2/channelN

Checklist

• [x] The code change is tested and works locally.
• [x] There is no commented out code in this PR.
• [x] No lint errors (use flake8)
• [x] 100% test coverage

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in as follows:
python3 -m venv apprise

# Change into our new directory
cd apprise

# Activate our virtual environment
source bin/activate

# Install the branch
pip install git+https://github.com/caronc/apprise.git@1057-revolt-tidy

# Test out the changes with the following command:
apprise -t "Test Title" -b "Test Message" \
  "revolt://credentials

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (6764590) 99.26% compared to head (6523e20) 99.27%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1062 +/- ## ========================================== + Coverage 99.26% 99.27% +0.01% ========================================== Files 136 136 Lines 17733 17738 +5 Branches 3616 3618 +2 ========================================== + Hits 17602 17610 +8 + Misses 120 119 -1 + Partials 11 9 -2 ```

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