Re-worked Telegram HTML/Markdown -> HTML Conversion

[caronc]

Description:

Related issue (if applicable): #changedetection.io/555, #573, #565, #566, #576, #572, and #577

This should complete the over-hall of Apprise/Telegram HTML support. Up until now Telegram Unit Tests and Usage pretty much worked well so long as the input provided into Apprise was text. But if the input provided was HTML or Markdown, there were very odd side effects.

The biggest problem is Telegram's HTML support isn't really HTML at all. It only supports <a>, <b>, <i>, and <code>.

This completed change attempts to handle most (hopefully through bulletproofing later, i'll get all) unsuported (Telegram) HTML tags (such as title, body, li, ul, etc, etc ) and convert them back to the closest supported tag (if not remove it all together). This change also attempts to respect block vs inline code and places new lines where applicable during the transformation.

Checklist

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

Testing

Anyone can help test this source code as follows:

# Create a virtual environment to work in
# This way you can just destroy it after when it's all over.
# The below will create a directory called apprise
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@more-html-conversion-support

# Run your telegram testing for HTML input:
apprise -i html  -t "<i>A Title</li>"  \
   -b "<p>a entry<div>another div entry</div></p>" \
    "tgram://credentials"

# or Markdown:
apprise -i markdown  -t "_A Title_"  \
   -b "[a link](http://localhost)" \
   "tgram://credentials"

[codecov-commenter]

Codecov Report

Merging #579 (969d81c) into master (3c07d80) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #579   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          109       109           
  Lines        14092     14094    +2     
  Branches      2636      2637    +1     
=========================================
+ Hits         14092     14094    +2     

Impacted Files	Coverage Δ
apprise/conversion.py	100.00% <100.00%> (ø)
apprise/plugins/NotifyTelegram.py	100.00% <100.00%> (ø)

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