Remove blob dependency in absorption

[cosimoNigro]

This PR removes the dependency, in the absorption class, from any Blob object.
More clearly, I have replaced
Absorption(blob, target, r) -> Absorption(target, r, z, mu_s)
z=0 by default and mu_s=1, such that one is automatically in the blazar scenario.

I have updated the documentation accordingly, I will comment in the pertaining issues where results have actually improved.

Incidentally, I have removed the crosscheck folder, and added it to the .gitignore.
I think it does not make sense to store all those pngs in github, they can be inspected locally after running the tests.
Additionally the check on the deviation from the reference models is performed automatically by np.allclose.

[sourcery-ai]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.78%.

Quality metrics	Before	After	Change
Complexity	1.02 ⭐	0.79 ⭐	-0.23 👍
Method Length	80.79 🙂	76.69 🙂	-4.10 👍
Working memory	14.61 😞	14.41 😞	-0.20 👍
Quality	62.42% 🙂	63.20% 🙂	0.78% 👍

Other metrics	Before	After	Change
Lines	1971	2100	129

Changed files	Quality Before	Quality After	Quality Change
agnpy/absorption/absorption.py	64.96% 🙂	69.15% 🙂	4.19% 👍
agnpy/compton/external_compton.py	56.10% 🙂	56.10% 🙂	0.00%
agnpy/targets/targets.py	64.37% 🙂	64.94% 🙂	0.57% 👍
agnpy/tests/test_absorption.py	60.83% 🙂	60.96% 🙂	0.13% 👍
agnpy/tests/test_compton.py	61.94% 🙂	61.06% 🙂	-0.88% 👎
agnpy/utils/conversion.py	84.45% ⭐	84.45% ⭐	0.00%

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
agnpy/compton/external_compton.py	ExternalCompton.evaluate_sed_flux_ss_disk	0 ⭐	260 ⛔	29 ⛔	39.42% 😞	Try splitting into smaller methods. Extract out complex expressions
agnpy/targets/targets.py	SSDisk.__init__	9 🙂	208 ⛔	14 😞	42.42% 😞	Try splitting into smaller methods. Extract out complex expressions
agnpy/compton/external_compton.py	ExternalCompton.evaluate_sed_flux_blr	0 ⭐	197 😞	27 ⛔	43.64% 😞	Try splitting into smaller methods. Extract out complex expressions
agnpy/absorption/absorption.py	Absorption.evaluate_tau_ss_disk	0 ⭐	233 ⛔	18 ⛔	45.35% 😞	Try splitting into smaller methods. Extract out complex expressions
agnpy/compton/external_compton.py	ExternalCompton.evaluate_sed_flux_dt	0 ⭐	182 😞	25 ⛔	45.37% 😞	Try splitting into smaller methods. Extract out complex expressions

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[codecov]

Codecov Report

Merging #76 (c599edd) into master (a3497b5) will increase coverage by 0.58%.
The diff coverage is 99.14%.

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   93.39%   93.97%   +0.58%     
==========================================
  Files          30       30              
  Lines        1725     1727       +2     
==========================================
+ Hits         1611     1623      +12     
+ Misses        114      104      -10     

Flag	Coverage Δ
unittests	93.97% <99.14%> (+0.58%)	⬆️

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

Impacted Files	Coverage Δ
agnpy/absorption/absorption.py	98.49% <98.66%> (+8.86%)	⬆️
agnpy/compton/external_compton.py	87.50% <100.00%> (ø)
agnpy/targets/targets.py	78.53% <100.00%> (-1.13%)	⬇️
agnpy/tests/test_absorption.py	100.00% <100.00%> (ø)
agnpy/tests/test_compton.py	100.00% <100.00%> (ø)
agnpy/utils/conversion.py	100.00% <100.00%> (ø)

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