Improve split and truncate overflow methods

[caronc]

Description:

Related issue (if applicable): #845

Improve ?overflow=split and ?overflow=truncate functionality to factor in the length of the title in it's calculations.

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 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@845-bodylen-overflow-improvement

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c240f8b) 99.27% compared to head (cf6c683) 99.27%.
Report is 1 commits behind head on master.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1035   +/-   ##
=======================================
  Coverage   99.27%   99.27%           
=======================================
  Files         135      135           
  Lines       17557    17574   +17     
  Branches     3583     3588    +5     
=======================================
+ Hits        17429    17446   +17     
  Misses        119      119           
  Partials        9        9           

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