reduce wait time on yahoo for repeated ISIN numbers

[Joren-vanGoethem]

add a local file or cache to save the found isin numbers to speed up conversion
cache only stays for the current run, file stays across runs

what do you think @dickwolff ?

[dickwolff]

Great suggestion. I have a cache of sorts in the current service but that does not work across multiple runs. Will look into that for sure!

[dickwolff]

@Joren-vanGoethem I added a cache solution in #22. The tool now stores it on disk and persists data between runs. On starting the tool, the data will be retrieved from cache and loaded in memory.

May need a more robust solution in the future if the cache becomes to large.

[dickwolff]

There was an issue with the TypeScript Map not being correctly processed and saved in cache. This is now resolved.

However there are now issues with retrieving symbols that are linked to the current "old" DEGIRO converter. This has to do with the way the current converter works with parsing records, and conflicting currencies. When #18 is merged, these issues should be resolved I believe.

[dickwolff]

I have made the final changes to the cache in #22 , which should work now 😀