Fix for filenames which contain regular expressions

[williamjameshandley]

Description

Filenames which contain regex characters (like '+') currently cannot be read.

PR introduces a failing test, which is fixed by changing one line to include an re.escape(...). I have also removed the .ranges files in the examples, since these are no longer used as of #212.

Checklist:

• I have performed a self-review of my own code
• My code is PEP8 compliant (flake8 anesthetic tests)
• My code contains compliant docstrings (pydocstyle --convention=numpy anesthetic)
• New and existing unit tests pass locally with my changes (python -m pytest)
• I have added tests that prove my fix is effective or that my feature works

[codecov]

Codecov Report

Merging #231 (4c2a1c1) into master (85d5243) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #231   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        26           
  Lines         2182      2182           
=========================================
  Hits          2182      2182           

Impacted Files	Coverage Δ
anesthetic/read/cobaya.py	100.00% <100.00%> (ø)
anesthetic/read/getdist.py	100.00% <100.00%> (ø)

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[lukashergt]

Looks good, please squash and merge.