Apprise API FORM based Attachment Support Added

[caronc]

Description:

Related issue (if applicable): #870 and apprise-api/39

FORM based Apprise API support (in addition to JSON that was already put in place in PR #873.

You can set which mode to use (FORM being the default as it is the most light weight), by specifying ?method= on the Apprise API URL.

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@apprise-attachment-support-pt2

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

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (1e30be3) 100.00% compared to head (c340293) 100.00%.

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Additional details and impacted files

@@            Coverage Diff            @@
##            master      #877   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          118       118           
  Lines        15572     15651   +79     
  Branches      3173      3200   +27     
=========================================
+ Hits         15572     15651   +79     

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

... and 3 files with indirect coverage changes

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