Cache codecogs equation rendering to avoid timeout errors

[apjanke]

About half the time I run make docs, it errors out due to a timeout on a codecogs web service query.

>> mlxshake_make docs
Exporting: MlxShake doc file: Tutorial.mlx
Exporting: /Users/janke/local/repos/MlxShake/docs-src/Tutorial.mlx -> /private/var/folders/_4/9mx5ryp52bb_z6drbcbrhwl40000gn/T/tpd7f7c402_3583_42c8_a38d_92d44747d285/Tutorial.tex
Exported:  /Users/janke/local/repos/MlxShake/docs-src/Tutorial.mlx -> /private/var/folders/_4/9mx5ryp52bb_z6drbcbrhwl40000gn/T/tpd7f7c402_3583_42c8_a38d_92d44747d285/Tutorial.tex
Exporting: /private/var/folders/_4/9mx5ryp52bb_z6drbcbrhwl40000gn/T/tpd7f7c402_3583_42c8_a38d_92d44747d285/Tutorial.tex -> /Users/janke/local/repos/MlxShake/docs/Tutorial.md
Error using websave (line 98)
The connection to URL
'https://latex.codecogs.com/gif.latex?%5Cbegin%7Barray%7D%7Bl%7D&space%3B%5Csin&space%3Bx=-%5Cint&space%3B%5Ccos&space%3Bxdx%5C%5C&space%3B%5Ccos&space%3Bx=%5Cint&space%3B%5Csin&space%3Bxdx&space%3B%5Cend%7Barray%7D' timed out
after 5.000 seconds. The reason is "Resolving timed out after 5103 milliseconds". Perhaps the server is not responding or weboptions.Timeout needs to be set to a higher value.
Error in janklab.mlxshake.internal.LsLatex2MardkownExporter>grabCodecogsEquationImage (line 538)
websave(file, codecogsUrl);
Error in janklab.mlxshake.internal.LsLatex2MardkownExporter>saveCodecogsRender (line 522)
grabCodecogsEquationImage(equationCode, file);
Error in janklab.mlxshake.internal.LsLatex2MardkownExporter>processEquations (line 489)
                [mdImgTag, eqnum] = saveCodecogsRender(eqncode, outImagesRelDir, outImagesDir, eqnum);
Error in janklab.mlxshake.internal.LsLatex2MardkownExporter/lslatex2markdown (line 154)
            str2md = processEquations(str2md, opts, inImagesRelDir, inImagesDir);
Error in janklab.mlxshake.lslatex2markdown (line 34)
outMdFile = exporter.lslatex2markdown(inFile, opts);
Error in janklab.mlxshake.exportlivescript (line 157)
            mdFile = janklab.mlxshake.lslatex2markdown(texFile, opts2);
Error in mlxshake_gendocs (line 42)
        janklab.mlxshake.exportlivescript(mlxFile, {'outFile', mdFile});
Error in mlxshake_make>build_docs (line 110)
mlxshake_gendocs(parts);
Error in mlxshake_make (line 40)
  build_docs(varargin) 
>> 

Mabye cache the codecogs results (safely) so this doesn't happen so often.