Add file format STP

[SylviaWhittle]

Closes #77

Adds .stp support.

@ns-rse In my haste I've kept everything in one function. Should I split the header reading code out into its own function? I'm of two minds about it at the moment.

Also please do point out if I've omitted documentation somewhere.

I:

• Added the function in stp.py
• Added the test in test_stp.py
• Added an example usage in example_01.ipynb
• Added documentation to README.md in the examples section and supported formats section.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.18182% with 12 lines in your changes missing coverage. Please review.

Project coverage is 74.88%. Comparing base (f282c31) to head (16caff8).
Report is 250 commits behind head on main.

Files with missing lines	Patch %	Lines
AFMReader/stp.py	78.18%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   65.87%   74.88%   +9.01%     
==========================================
  Files           3        9       +6     
  Lines         337      661     +324     
==========================================
+ Hits          222      495     +273     
- Misses        115      166      +51     

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[ns-rse]

Relatively quick scan through as its after hours. Some minor comments on how we could perhaps keep things shorter without making it harder to understand. Possibly an extraneous notebook has crept in.

Don't think there is a huge need to abstract the header reading out to its own function unless you really wanted to.

Challenging thing is having example files that fail the tests. Mocking might be of use here but I appreciate its a fair amount of work and your busy.

[ns-rse]

Not on the ball, sorry for the delay 👍