Fix Markdown parsing for Telegram

[luckydonald]

See https://github.com/caronc/apprise/issues/740#issuecomment-2045907365, fixes #740.

Description:

Related issue (if applicable): #740

Markdown (v1) has bugs and is superseded by MarkdownV2.

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@<this.branch-name>

# Test out the changes with the following command:
apprise -t "Test Title" -b "Test Message" \
  <apprise url related to ticket>

[caronc]

Added new varible ?mdv= which can optionally be set on the telegram:// Apprise URL supporting both v1 and v2, but defaulting to v2 going forward (thanks to this PR).

Probably a bit of overkill, but for those who might be expecting a specific look and feel, they'll be able to at least fall back to that, otherwise it leverages the new version (2).

Thank you very much for this PR!! :rocket: :+1: