Move common functions in example scripts into new module

[bwohlberg]

Move some common functions in example scripts into new scico.examples module.

Also:

• Fix docstrings in scico.data
• Trivial docstring edits in examples/scripts/ct_astra_weighted_tv_admm.py
• For deconv_microscopy_... examples:
  • Changed downsampling rate to 2 (see *)
  • Downsampling rate is no longer required to be even
  • Changed path of cached EPFL BIG data to ~/.cache/scico/examples

(*) Running on GPU may now require setting the XLA environment variables

export XLA_PYTHON_CLIENT_ALLOCATOR=platform
export XLA_PYTHON_CLIENT_PREALLOCATE=false

[codecov]

Codecov Report

Merging #151 (9d95dd6) into main (912bb9e) will increase coverage by 0.00%.
The diff coverage is 92.59%.

@@           Coverage Diff           @@
##             main     #151   +/-   ##
=======================================
  Coverage   92.16%   92.16%           
=======================================
  Files          47       48    +1     
  Lines        3240     3294   +54     
=======================================
+ Hits         2986     3036   +50     
- Misses        254      258    +4     

Flag	Coverage Δ
unittests	92.16% <92.59%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
scico/data/__init__.py	100.00% <ø> (ø)
scico/examples.py	92.59% <92.59%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 912bb9e...9d95dd6. Read the comment docs.